Pulmonary atresia is a congenital heart defect present at birth in which the pulmonary valve fails to form properly, completely obstructing blood flow from the right ventricle to the lungs and requiring alternative pathways such as a patent ductus arteriosus to maintain pulmonary circulation.

Pulmonary Atresia in Children

Pulmonary atresia (PA) refers to a group of congenital heart defects characterised by complete obstruction (atresia) of the pulmonary valve or right ventricular outflow tract (RVOT), preventing any direct antegrade flow of blood from the right ventricle into the pulmonary arteries.

Breaking down the name:

"Pulmonary" = relating to the lungs / pulmonary artery
"Atresia" = from Greek a- (without) + tresis (perforation) — meaning an absent or imperforate opening

This is a duct-dependent lesion in the majority of cases: the neonate relies on a patent ductus arteriosus (PDA) to supply blood to the lungs. Once the ductus closes (typically within 10–15 hours to days of birth), the infant rapidly deteriorates with profound cyanosis, metabolic acidosis, and death if untreated ^[1].

Key concept: Pulmonary atresia is not a single disease. It is classified into two fundamentally different entities based on the presence or absence of a ventricular septal defect (VSD), because the embryology, anatomy, pathophysiology, management, and prognosis differ dramatically between the two.

Feature	PA with Intact Ventricular Septum (PAIVS)	PA with VSD (PAVSD / TOF-PA)
Incidence	4–8 per 100,000 live births	0.7 per 10,000 live births
Proportion of all CHD	1–3%	~1–2%
Sex ratio	M:F = 1:1	M:F ≈ 1:1
Association with other anomalies	Rarely a/w extracardiac anomalies	50% associated with right-sided aortic arch; a/w 22q11.2 deletion (DiGeorge syndrome)

In Hong Kong, congenital heart disease affects approximately 8–10 per 1,000 live births ^[2]. Given HK's low birth rate (~35,000–40,000 births/year), pulmonary atresia remains rare but is a critical diagnosis in neonatal units. The universal pulse oximetry screening programme (now standard in many Hong Kong hospitals) is designed to catch exactly these duct-dependent lesions before catastrophic ductal closure.

Risk Factors

Genetic/chromosomal: 22q11.2 microdeletion (especially PAVSD), trisomy 21, trisomy 18
Maternal factors: uncontrolled diabetes mellitus, phenylketonuria, rubella, alcohol, retinoic acid exposure, anticonvulsants (valproate, phenytoin)
Family history: ~2–4% recurrence risk in siblings for CHD in general; higher if first-degree relative affected
Multifactorial inheritance: most cases are sporadic with multifactorial aetiology

PAVSD: strongly associated with 22q11.2 deletion (velocardiofacial / DiGeorge syndrome) — always screen for this in any child with PA + VSD + MAPCAs
PAIVS: generally sporadic; no strong single-gene association, but some cases linked to transcription factor mutations (e.g., NKX2.5)

Anatomy and Embryology

During embryonic development (weeks 3–8), the truncus arteriosus is septated by the aorticopulmonary (AP) septum (also called the conotruncal or bulbar septum) into the ascending aorta and pulmonary trunk. This septum grows in a spiral fashion, which is why the aorta and pulmonary artery normally wind around each other.

Simultaneously:

The conus (infundibulum) is remodelled to form the subvalvar outflow tracts
The semilunar valves (aortic and pulmonary) develop from endocardial cushion tissue
The interventricular septum grows upward and fuses with the bulbar septum to close the VSD

What goes wrong in Pulmonary Atresia

This is fundamentally an extreme variant of Tetralogy of Fallot (TOF) with complete atresia of the pulmonary valve ^[1]^[3]
The bulbar septum deviates excessively anteriorly and cephalad → severe narrowing/complete obliteration of the RVOT → atretic pulmonary valve
The septum fails to fuse with the interventricular septum → large, non-restrictive VSD (malalignment type)
The aorta overrides the VSD
Because no antegrade flow reaches the pulmonary arteries in fetal life, the native pulmonary arteries may be hypoplastic or even absent
Major aortopulmonary collateral arteries (MAPCAs) develop as alternative blood supply to the lungs

The ventricular septum is intact (no VSD)
The pulmonary valve is imperforate (fused commissures forming a membrane) or there is complete muscular obliteration of the infundibulum ^[1]
Because there is no exit for blood from the RV:
- The RV becomes hypertrophied and hypoplastic (pressure overload with no volume work)
- The tricuspid valve is small (hypoplastic) and often incompetent ^[1]
- In ~1/3 of cases, abnormal connections develop between the hypertensive RV cavity and the coronary arteries → right ventriculo-coronary sinusoidal (fistulous) communications ^[1]

Critical Concept: RV-Dependent Coronary Circulation (RVDCC)

In approximately 1/4 of patients with ventriculo-coronary fistulae, there is stenosis of the coronary artery proximal to the fistulous connection. This means the coronary arteries receive their blood supply retrogradely from the high-pressure RV rather than from the aorta. This is called RV-dependent coronary circulation (RVDCC) ^[1].

Why this matters: If you decompress the RV (e.g., by opening the pulmonary valve or creating an RV-PA conduit), the RV pressure drops, coronary perfusion pressure falls, and the patient can develop myocardial ischaemia and sudden death. These patients CANNOT undergo biventricular repair and must be directed toward a single-ventricle (Fontan) pathway. This is a must-know concept for exams.

Structure	Role in PA	What happens when it closes
Patent Ductus Arteriosus (PDA)	Sole or major source of pulmonary blood flow (in PAIVS always; in PAVSD without adequate MAPCAs)	Profound cyanosis, metabolic acidosis, death
Patent Foramen Ovale (PFO) / ASD	Allows obligatory R→L shunting in PAIVS (decompresses RA/RV)	If restrictive → severe RA hypertension, low cardiac output
MAPCAs (in PAVSD)	Alternative pulmonary blood supply arising from descending aorta	Variable — may be adequate, inadequate, or excessive

Aetiology (with Hong Kong focus) and Pathophysiology

Pulmonary atresia is classified into two main types ^[1]^[3]:

A. Pulmonary Atresia with VSD (PAVSD / TOF with Pulmonary Atresia)

Complete RVOT obstruction → no antegrade flow from RV to PA
The large, non-restrictive VSD allows obligatory R→L shunting at the ventricular level → all systemic venous blood goes from RV → across VSD → into the overriding aorta ^[1]
Pulmonary blood supply depends entirely on:
- Ductus arteriosus (especially in neonatal period)
- Major aortopulmonary collateral arteries (MAPCAs) ^[1]

MAPCAs develop early in embryonic life and normally regress as the native pulmonary arteries develop. If the pulmonary arteries fail to develop normally (as in PAVSD), these collaterals persist and become the main blood supply to the lungs ^[1].

Key points about MAPCAs:

Arise from the descending thoracic aorta (most commonly), subclavian, or bronchial arteries
Supply different lung segments — some segments may be supplied by native PAs, others only by MAPCAs (this is called dual supply)
If MAPCAs are stenosed or inadequate → insufficient pulmonary blood flow → cyanosis ± shock upon ductal closure ^[1]
If MAPCAs are unrestricted → excessive pulmonary blood flow → pulmonary hypertension (because systemic-pressure blood flows directly into lungs) → heart failure ^[1]
This creates a paradox: the same patient can have some lung segments that are over-perfused and others that are under-perfused

"Stenosed/inadequate collaterals → inadequate pulmonary blood flow → present with cyanosis ± shock upon closure of duct. Unrestricted collaterals → excessive pulmonary blood flow → present with heart failure." ^[1]

Mixed venous and systemic blood in the aorta → desaturated blood in systemic circulation
Degree of cyanosis is inversely proportional to the amount of pulmonary blood flow
Degree of heart failure is directly proportional to pulmonary blood flow

B. Pulmonary Atresia with Intact Ventricular Septum (PAIVS)

Imperforate pulmonary valve or muscular infundibular obliteration → no exit for RV blood ^[1]
Severe RV pressure overload → RV pressure may be suprasystemic (RVP > LVP)
The RV has no volume outlet → the RV becomes hypertrophied and hypoplastic (small cavity, thick walls) ^[1]
Blood can only leave the right heart via:
- Obligatory R→L shunting through the PFO (RA → LA) — this is the main route
- Tricuspid regurgitation back into RA → then via PFO to LA
- Ventriculo-coronary sinusoidal connections (in ~1/3) → RV empties into coronary arteries → retrograde flow into aortic root ^[1]
Duct-dependent pulmonary circulation: the only source of pulmonary blood flow is via the PDA (aorta → DA → PA) ^[1]
Upon ductal closure: catastrophic reduction in pulmonary blood flow → profound cyanosis → metabolic acidosis → death ^[1]

Duct-Dependent Lesions — Must Recognise Postnatally

"Duct-dependent pulmonary circulation → important to recognize postnatally as they are invariably fatal if untreated" ^[1]. The median survival without intervention is only days to weeks. ~50% die within 2 weeks, 85% die by 6 months if untreated ^[1].

The first-line treatment upon suspicion is IV prostaglandin E1 (PGE1, alprostadil) to keep the ductus arteriosus open.

The RV in PAIVS exists on a spectrum from:

Well-developed RV (tripartite: inlet + trabecular + infundibular portions all present) → may be suitable for biventricular repair
Moderately hypoplastic RV (bipartite: inlet + trabecular only) → may need staged approach
Severely hypoplastic RV (unipartite: inlet only) → single-ventricle pathway (Fontan)

The size of the tricuspid valve annulus correlates with RV size and is used to predict whether biventricular repair is feasible.

Feature	PAIVS	PAVSD (TOF/PA)
VSD	Absent (intact septum)	Present (large, malalignment type)
RV morphology	Hypertrophied, hypoplastic	Usually well-developed (similar to TOF)
Tricuspid valve	Small and incompetent	Usually normal or mildly abnormal
Pulmonary blood supply	PDA only (duct-dependent)	PDA ± MAPCAs
Coronary abnormalities	Ventriculo-coronary fistulae in ~1/3; RVDCC in ~1/4 of these	Not typical
Overriding aorta	No	Yes
Relationship to TOF	Distinct entity	Extreme variant of TOF
CXR appearance	Variable heart size; diminished pulmonary vascular markings	Boot-shaped heart; oligaemic or uneven lung fields
Surgical pathway	Single ventricle (Fontan) if severe hypoplasia/RVDCC; biventricular if adequate RV	Unifocalisation of MAPCAs + VSD closure + RV-PA conduit

Clinical Features

A. Symptoms

Cyanosis appears within a few hours after birth ^[1]

Pathophysiological basis:

In PAIVS: Obligatory R→L shunt at the atrial level (deoxygenated systemic venous blood passes through PFO into LA → mixes with oxygenated pulmonary venous blood → enters LV → aorta) ^[1]
In PAVSD: R→L shunt at the ventricular level (deoxygenated blood passes through VSD into overriding aorta)
The degree of cyanosis is inversely proportional to the amount of pulmonary blood flow
In PAIVS, the degree of cyanosis depends on the size of the arterial duct ^[1] — as the duct constricts, less blood reaches the lungs, and cyanosis worsens
In PAVSD, the severity depends on the amount of aortopulmonary collaterals ^[1]

Clinical pearl: Cyanosis that does not improve with supplemental oxygen (the hyperoxia test — PaO2 remains < 150 mmHg on 100% FiO2) strongly suggests a cardiac cause rather than respiratory disease. An oligaemic lung field on CXR supports cyanotic CHD over respiratory disease ^[4].

"Rapid clinical deterioration after ductal closure → uniformly fatal if untreated" ^[1]

Pathophysiological basis:

The PDA is the sole source of pulmonary blood flow
Ductal closure (triggered by ↑PaO2 and ↓PGE2 after birth) removes pulmonary blood supply
Leads to:
- Severe metabolic acidosis (tissue hypoxia → anaerobic metabolism → lactic acid)
- Profound hypoxaemia
- Seizures (cerebral hypoxia) ^[1]
- Cardiogenic shock, cardiac arrest, and death ^[1]

In PAIVS: SOB (less common) in those with severe TR ^[1] — because massive tricuspid regurgitation causes RA dilation and systemic venous congestion
In PAVSD with unrestricted MAPCAs: excessive pulmonary blood flow causes pulmonary overcirculation and left heart volume overload → congestive heart failure ^[1]
- These infants may present with tachypnoea, feeding difficulty, failure to thrive, and hepatomegaly rather than prominent cyanosis

Common in any infant with significant cardiac disease
Mechanism: ↑metabolic demand (tachypnoea, increased cardiac work) + ↓caloric intake (poor feeding due to breathlessness) + ↓oxygen delivery to tissues

B. Signs

Sign	Pathophysiological Basis
Cyanosis	Obligatory R→L shunt at atrial level; degree depends on PDA size ^[1]
LV impulse (prominent)	LV supplies both systemic and pulmonary circulations (the LV effectively does all the work since RV has no output) ^[1]
NO RV impulse	RV usually atrophic/hypoplastic due to atretic pulmonary outflow — the RV is a high-pressure, low-volume chamber with no stroke volume ^[1]
Single S2	Only one semilunar valve (aortic) is functional — the pulmonary valve is atretic, so there is no P2 component ^[1]
Pansystolic murmur (PSM) at LLSB	From tricuspid regurgitation — the incompetent, small TV allows backward leak during systole ^[1]
Soft systolic or continuous murmur	From PDA — flow from aorta through the ductus into pulmonary artery ^[1]
Hepatomegaly	If significant TR → RA/RV congestion → hepatic venous congestion

Sign	Pathophysiological Basis
Cyanosis	R→L shunt across VSD; severity depends on pulmonary blood flow ^[1]
RV impulse may be present	RV is typically better developed in PAVSD (unlike PAIVS)
Single S2	No pulmonary valve → no P2
No PS murmur (unlike TOF)	"Signs: similar to TOF but no PS murmur" ^[1] — in TOF, the ejection systolic murmur (ESM) at LUSB is caused by blood flowing through the stenosed (but patent) RVOT; in PA, there is no flow at all → no murmur from RVOT
Continuous collateral murmur	"± continuous collateral murmur in those with abundant aortopulmonary collaterals" ^[1] — blood flows through MAPCAs from aorta to pulmonary vasculature continuously throughout the cardiac cycle
Soft PDA murmur	If ductus is patent

High Yield: Why is there no RVOT murmur in PA?

In TOF, the ESM at the LUSB is caused by turbulent flow through the narrowed (but patent) RVOT. In pulmonary atresia, the RVOT is completely occluded — no flow = no murmur. This is a key distinguishing feature. In fact, during a Tet spell in TOF, the murmur decreases as flow through the RVOT decreases; if the murmur disappears entirely, it essentially means the RVOT is functionally atretic — an ominous sign ^[3].

Feature	TOF	PAVSD	PAIVS
S2	Single (soft/absent P2)	Single	Single
ESM at LUSB (PS murmur)	Present (hallmark)	Absent	Absent
PSM at LLSB (VSD/TR)	VSD murmur soft (large defect)	May be present	PSM from TR
Continuous murmur	Absent (unless BT shunt)	MAPCAs	PDA

A neonate presenting with:

Cyanosis within hours of birth
Not improving with supplemental O2 (failed hyperoxia test)
Oligaemic lung fields on CXR
Single S2
No PS murmur

→ Think pulmonary atresia (differentiate PAIVS vs PAVSD by presence/absence of VSD on echo)

AOS Exam Point

"Which of the following piece of clinical information SUPPORTS cyanotic congenital heart disease rather than respiratory disease as the cause of cyanosis? → Radiograph showing an oligaemic lung field due to reduced pulmonary blood flow" ^[4]. This is because respiratory disease typically shows lung parenchymal changes ± plethoric fields (atelectasis, consolidation), whereas cyanotic CHD with reduced pulmonary flow shows oligaemic lungs.

Investigations (Preview)

Full investigation and diagnostic algorithm will be covered in the next section. Key points to preview:

Investigation	Findings
CXR	Heart size normal or enlarged; grossly enlarged RA/RV due to TR; diminished pulmonary vascular markings
ECG	RA dilation (P pulmonale); LV dominance with paucity of RV forces
Echo	Delineate type of PA (valvular vs infundibular); degree of RV hypoplasia; detect abnormal Rt ventriculo-coronary sinusoidal flow

Investigation	Findings
CXR	Boot-shaped heart; oligaemic lung fields with ductal constriction or stenosed collaterals; uneven pulmonary vascularity depending on course, site, size of collaterals
ECG	Right axis deviation and RVH
Echo	Atretic RV outflow with RVH and VSD; aortopulmonary collateral flow → detailed delineation only by MRI, cardiac catheterization

Why is the ECG different between PAIVS and PAVSD?

PAIVS: The RV is hypoplastic with minimal muscle mass → paucity of RV forces on ECG; the LV does all the work → LV dominance
PAVSD: The RV is well-developed and hypertrophied (ejects blood through the VSD against systemic pressure, similar to TOF) → RAD and RVH

This ECG distinction is frequently tested!

Syndrome	Associated PA type	Key features to look for
22q11.2 deletion (DiGeorge/Velocardiofacial)	PAVSD with MAPCAs (most classic association)	Hypocalcaemia, T-cell immunodeficiency, palatal abnormalities, facial dysmorphism
Alagille syndrome (JAG1 mutation)	Peripheral pulmonary stenosis → can be a/w PA	Bile duct paucity, cholestasis, butterfly vertebrae, posterior embryotoxon
CHARGE syndrome	Various conotruncal defects including PA	Coloboma, Heart defect, Atresia choanae, Retardation of growth, Genital anomalies, Ear anomalies
Trisomy 18 (Edwards)	Various CHD	Clenched fists, rocker-bottom feet, severe intellectual disability

High Yield Summary

Pulmonary Atresia — Key Points for Exams:

Two distinct entities: PAIVS (no VSD, hypoplastic RV, duct-dependent) vs PAVSD (VSD present, extreme TOF variant, ± MAPCAs)
Both are duct-dependent cyanotic heart diseases → present with cyanosis within hours of birth; failed hyperoxia test; oligaemic lung fields
PAIVS: Single S2, NO RV impulse (LV impulse instead), PSM from TR, soft PDA murmur; ECG shows LV dominance; 1/3 have ventriculo-coronary fistulae; 1/4 of those have RVDCC (precludes biventricular repair)
PAVSD: Single S2, NO PS murmur (unlike TOF), ± continuous MAPCA murmur; ECG shows RAD + RVH; boot-shaped heart on CXR
Immediate management: IV prostaglandin E1 (alprostadil) to maintain ductal patency
PAIVS mortality without treatment: ~50% by 2 weeks, 85% by 6 months
MAPCAs in PAVSD: if stenosed → cyanosis/shock; if unrestricted → pulmonary hypertension/HF
CXR clue for cyanotic CHD vs respiratory: oligaemic lung fields + cyanosis = cardiac cause
ECG distinction: PAIVS = LV dominance; PAVSD = RVH + RAD
RVDCC = contraindication to biventricular repair → must go Fontan pathway

Active Recall - Pulmonary Atresia: Definition, Epidemiology, Pathophysiology and Clinical Features

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 215–222) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf ^[3] Senior notes: Ryan Ho Cardiology.pdf (pages 187–193) ^[4] AOS material: AOS - Paeds.pdf (Question 6)

Differential Diagnosis of Pulmonary Atresia

The clinical scenario you are faced with is almost always a neonate presenting with cyanosis in the first hours to days of life. The differential diagnosis therefore centres on:

Other cyanotic congenital heart diseases — the main DDx challenge, because many share similar presentations (duct-dependent cyanosis, single S2, oligaemic lung fields)
Non-cardiac causes of neonatal cyanosis — respiratory disease, sepsis, metabolic, persistent pulmonary hypertension of the newborn (PPHN)
Once cyanotic CHD is established — differentiating between the specific cardiac lesions

The key clinical question is: "Is this cyanosis cardiac or non-cardiac?" and if cardiac, "What specific lesion?"

GC Lecture High Yield — Categorisation of Cyanotic CHD

Cyanotic CHD can be categorised according to the underlying physiology ^[5]:

↓ Pulmonary blood flow (oligaemic lung fields)
↑ Pulmonary blood flow (plethoric lung fields)
Severe heart failure

This classification is the single most important framework for the DDx of a cyanotic neonate because it determines the entire diagnostic and management pathway.

Before diving into specific cardiac lesions, you must first determine whether the cyanosis is of cardiac origin or not. This distinction is critical and frequently tested.

Feature	Cardiac Cyanosis	Respiratory / Non-Cardiac Cyanosis
Response to O₂ (Hyperoxia test)	PaO₂ typically remains < 100–150 mmHg on 100% FiO₂	PaO₂ usually rises > 150 mmHg (often > 200)
CXR lung fields	Oligaemic (↓ pulm blood flow) or plethoric (↑ pulm blood flow) but relatively clear parenchyma	Parenchymal disease (consolidation, ground glass, atelectasis)
Respiratory effort	Tachypnoea often without significant retractions (quiet tachypnoea)	Marked retractions, grunting, nasal flaring
Heart murmur	May or may not be present	Absent (unless coincidental)
SpO₂ pre-ductal vs post-ductal	May show differential (especially TGA, CoA)	Usually no differential

"Radiograph showing an oligaemic lung field due to reduced pulmonary blood flow SUPPORTS cyanotic congenital heart disease rather than respiratory disease as the cause of cyanosis" ^[4]. This was directly tested in AOS.

Non-cardiac DDx of neonatal cyanosis [6]

Category	Examples	Distinguishing features
Respiratory disorders	Surfactant deficiency (RDS), meconium aspiration syndrome, pulmonary hypoplasia	CXR parenchymal changes; responds to O₂; respiratory distress prominent
Persistent pulmonary hypertension of the newborn (PPHN)	Idiopathic, secondary to MAS, CDH, sepsis	Pre/post-ductal SpO₂ difference > 5–10%; labile oxygenation; Echo shows R→L shunt at DA/PFO with structurally normal heart
Infection	Group B Streptococcal septicaemia	Fever/hypothermia, poor perfusion, raised CRP/WCC; maternal GBS risk factors
Metabolic	Inborn errors of metabolism → metabolic acidosis and shock	Severe acidosis disproportionate to clinical picture; hyperammonaemia; abnormal metabolic screen
Haematological	Methaemoglobinaemia, polycythaemia	Characteristic chocolate-brown blood (metHb); high Hct (polycythaemia)
Neurological	Central hypoventilation, birth asphyxia	Apnoea > cyanosis; abnormal tone/reflexes

PPHN vs Cyanotic CHD — A Critical Distinction

PPHN can mimic cyanotic CHD very closely: both cause cyanosis unresponsive to O₂ and both have R→L shunting. The key differentiator is echocardiography — PPHN shows a structurally normal heart with elevated pulmonary artery pressure and R→L shunting across PDA/PFO, whereas cyanotic CHD shows a structural cardiac anomaly. A pre/post-ductal SpO₂ difference of > 5–10% is more characteristic of PPHN (or lesions with ductal-level shunting like coarctation) than of intracardiac shunts.

Step 2: Within Cyanotic CHD — Categorise by Pulmonary Blood Flow

Once you have established a cardiac cause, the next step is to look at the CXR lung fields to categorise the physiology:

These are the lesions most relevant to the DDx of pulmonary atresia, because both PAIVS and PAVSD typically present with oligaemic lung fields (reduced pulmonary vascular markings).

The key differentials with decreased pulmonary blood flow are ^[5]^[7]:

Diagnosis	Ductal Dependence	Key Distinguishing Features
Tetralogy of Fallot (TOF)	√/✗ (only if severe RVOT obstruction) ^[5]	ESM at LUSB from PS (present, unlike PA); variable cyanosis timing (usually progressive over months unless severe); boot-shaped heart; Tet spells with squatting in older children ^[3]
TOF with Pulmonary Atresia (PAVSD)	√ ^[5]	No PS murmur (vs TOF); boot-shaped heart; continuous MAPCA murmur possible; RAD + RVH on ECG ^[1]
PA with Intact Ventricular Septum (PAIVS)	√ ^[5]	No RV impulse; LV dominance on ECG; PSM from TR; single S2; RV hypoplasia on Echo ^[1]
Critical Pulmonary Stenosis	√ (only in critical PS) ^[5]	Very similar to PAIVS but valve is not completely atretic — a tiny jet of antegrade flow can be detected on colour Doppler Echo; amenable to balloon dilation via cardiac catheterisation ^[7]
Tricuspid Atresia	√/✗ (only if severe RVOT obstruction) ^[5]	NO communication between RA and RV → total and obligatory atrial R→L shunt ^[7]; "superior" QRS axis (left axis deviation) on ECG is classic; small/absent RV on Echo
Tricuspid Stenosis	✗ ^[5]	Atrial R→L shunt; less severe than TA; rare in isolation
Ebstein's Anomaly	√/✗ (only if severe RVOT obstruction) ^[5]	Malformed and downward displacement of tricuspid valve leaflets → severe TR → RA enlargement ^[7]; massive cardiomegaly on CXR ("wall-to-wall" heart); WPW pattern on ECG in ~20%

High Yield: How to tell PA from Critical PS

Critical pulmonary stenosis is essentially at the mild end of the PAIVS spectrum — the valve is not completely atretic but is so severely stenosed that there is near-total obstruction. Clinically, the two are almost indistinguishable. The critical distinction is on echocardiography: in critical PS, colour Doppler shows a tiny antegrade jet across the pulmonary valve; in PAIVS, there is absolutely no antegrade flow. This matters because critical PS is amenable to balloon dilation of the pulmonary valve via cardiac catheterisation ^[7], which can convert a single-ventricle pathway into a biventricular one.

These lesions cause cyanosis because of abnormal mixing of systemic and pulmonary venous blood, but the total pulmonary blood flow is actually increased (plethoric lung fields on CXR). They are less likely to be confused with pulmonary atresia but must be considered in the broader DDx of neonatal cyanosis ^[5]:

Diagnosis	Ductal Dependence	Key Distinguishing Features
Transposition of Great Arteries (TGA)	√ ^[5]	Two parallel circulations — the aorta arises from RV and PA from LV; "egg-on-a-string" heart on CXR; narrow mediastinum; plethoric lung fields; profound cyanosis hours after birth with relatively little respiratory distress
Truncus Arteriosus	✗ (no mixing required) ^[5]	Single arterial trunk giving rise to both aorta and PA; VSD always present; bounding pulses; continuous murmur; plethoric lungs; a/w 22q11.2 deletion
Total Anomalous Pulmonary Venous Return (TAPVR)	✗ (no mixing required) ^[5]	All pulmonary veins drain into systemic venous system rather than LA; "snowman" (figure-of-eight) sign on CXR in supracardiac type; if obstructed → pulmonary oedema + severe cyanosis resembling RDS

These present primarily with shock and heart failure rather than isolated cyanosis, but peripheral cyanosis and poor perfusion can mimic cyanotic CHD ^[5]:

Diagnosis	Ductal Dependence	Key Distinguishing Features
Coarctation of Aorta	√ (only in critical coarctation) ^[5]	BP discrepancy between upper and lower limbs; weak femoral pulses; cardiogenic shock D4–7; oliguria as first presentation ^[6]
Interrupted Aortic Arch	√ ^[5]	Complete discontinuity of aortic arch; catastrophic collapse with ductal closure; a/w 22q11.2 deletion
Critical Aortic Stenosis	√ (only in critical AS) ^[5]	Systolic murmur at RUSB radiating to carotids; LVH; poor LV function
Hypoplastic Left Heart Syndrome (HLHS)	√ ^[5]	Not common in Hong Kong / Chinese population, but major in Caucasians ^[6]; underdeveloped LV, aorta, mitral valve; single S2; grey/mottled appearance; absent LV impulse

Once pulmonary atresia is suspected (or confirmed on echo), the next DDx question is: Is this PAIVS or PAVSD? This is not just academic — it fundamentally changes the management strategy.

Feature	PAIVS	PAVSD (TOF/PA)
VSD	Absent	Present (large, malalignment)
RV	Hypertrophied and hypoplastic ^[1]	Well-developed, hypertrophied
Tricuspid valve	Small and incompetent	Usually normal
Coronary abnormalities	Ventriculo-coronary fistulae in 1/3 ^[1]	Not typical
Pulmonary blood supply	PDA only	PDA + MAPCAs ^[1]
ECG	LV dominance, paucity of RV forces, P pulmonale ^[1]	RAD, RVH ^[1]
CXR	Normal/enlarged heart; diminished PVM	Boot-shaped heart; oligaemic or uneven PVM ^[1]
Auscultation	PSM at LLSB (TR); soft PDA murmur ^[1]	No PS murmur; ± continuous MAPCA murmur ^[1]
Echo	Atretic PV, hypoplastic RV, intact septum, ± sinusoidal flow	Atretic RVOT, VSD, ± hypoplastic native PAs

Specific DDx Comparisons — Why Each Mimic is Different

This is the most important comparison, because PAVSD is literally an extreme variant of TOF ^[1]^[7].

Feature	TOF	PAVSD	PAIVS
RVOT	Stenosed (patent)	Completely atretic	Completely atretic
PS murmur (ESM at LUSB)	Present — hallmark murmur	Absent — no flow through RVOT ^[1]	Absent
VSD	Present	Present	Absent
Timing of cyanosis	Variable — often progressive over months (infundibular hypertrophy worsens)	Hours after birth (duct-dependent)	Hours after birth (duct-dependent)
Tet spells	Characteristic	Not typical (no dynamic RVOT to spasm)	Not applicable
ECG	RAD, RVH	RAD, RVH	LV dominance

Why no Tet spells in PA? In TOF, the Tet (hypercyanotic) spell occurs because of dynamic spasm of the infundibular muscle, which transiently worsens RVOT obstruction. In PA, the RVOT is already completely occluded — there is no dynamic component to worsen. The obstruction is fixed and maximal.

Both involve obstruction of flow through the right heart, but at different levels.

Feature	PA (PAIVS)	Tricuspid Atresia
Level of obstruction	Pulmonary valve / RVOT	Tricuspid valve
Communication RA↔RV	Present (via incompetent TV)	Absent — NO communication between RA and RV ^[7]
R→L shunt level	Atrial (via PFO)	Atrial (obligatory, total) ^[7]
RV	Hypertrophied, hypoplastic	Severely hypoplastic / absent (no inflow)
ECG axis	Normal or right	Left axis deviation / superior axis (classic — because the LV is dominant and conduction goes through the left bundle)
VSD	Absent	Often present (and determines pulmonary flow)

Why is the ECG axis different? In PAIVS, the RV exists (albeit hypoplastic) and receives some flow via TR — it still contributes some electrical forces. In tricuspid atresia, the RV is essentially absent, so the entire QRS is generated by the LV → dominant leftward and superior forces → left axis deviation. This is one of the few cyanotic CHDs with LAD and is a classic exam distinguisher.

Feature	PA (PAIVS)	Ebstein's Anomaly
Tricuspid valve	Small and incompetent ^[1]	Malformed, downward displacement of leaflets → RVOT obstruction due to "atrialised" RV ^[7]
RA size	Enlarged (due to TR)	Massively enlarged ("wall-to-wall" heart on CXR)
ECG	P pulmonale; LV dominance	Tall P waves; RBBB; WPW in ~20% (accessory pathway)
Cyanosis	Usually severe, duct-dependent	Variable — depends on degree of functional RVOT obstruction
Murmur	PSM (TR)	PSM (TR) — but may also hear a scratchy systolic sound
CXR	Variable heart size	Massive cardiomegaly — disproportionate to symptoms

Why WPW in Ebstein's? The abnormal insertion of the tricuspid valve leaflets can disrupt the normal fibrous annulus that electrically insulates atria from ventricles, allowing accessory pathways (bundles of Kent) to form → pre-excitation → WPW pattern.

Feature	PA (either type)	D-TGA
Pulmonary blood flow	Decreased	Increased (plethoric)
CXR lung fields	Oligaemic	Plethoric
CXR heart shape	Boot-shaped (PAVSD) or variable (PAIVS)	"Egg on a string" (narrow mediastinum)
Pathophysiology	R→L shunt with reduced pulm flow	Two parallel circulations — requires mixing (PFO, VSD, PDA) to survive
S2	Single	Single (A2 is posterior and inaudible)
Duct dependence	For pulmonary blood flow	For mixing between circulations

"5 Ts + E-P" (or think of the right heart from valve to valve):

Tetralogy of Fallot
TOF with PA (= PAVSD)
Tricuspid atresia
Tricuspid stenosis (rare)
(T) = critical Pulmonary stenosis (the "P" sounds like "T" if you squint — or just add it)
Ebstein's anomaly
Pulmonary atresia with IVS

All of these share a common theme: obstruction to blood flow through the right heart → reduced pulmonary blood flow → deoxygenated blood shunted to systemic circulation → cyanosis.

When you see pulmonary atresia or related cyanotic CHD, always think about associated syndromes, because the dysmorphic features can point you toward the diagnosis ^[3]:

Syndrome	Cardiac lesion	Clinical clue
22q11.2 deletion (DiGeorge)	PAVSD with MAPCAs, interrupted aortic arch, truncus arteriosus, TOF	Hypocalcaemia, absent thymic shadow on CXR, palatal anomalies
Down syndrome (Trisomy 21)	AVSD, VSD, ASD, TOF	Characteristic facies, hypotonia, single palmar crease
Noonan syndrome	Valvular PS with dysplastic valve, ASD, HCM	Turner-like phenotype, right-sided cardiac lesions ^[3]
Williams syndrome	Supravalvular AS, peripheral PS	Elfin facies, hypercalcaemia, mental retardation
Turner syndrome	Left-sided lesions — CoA, bicuspid AV, AS	Short stature, webbed neck, wide-spaced nipples ^[3]
Alagille syndrome	Peripheral pulmonary stenosis, can be a/w PA	Bile duct paucity, butterfly vertebrae, posterior embryotoxon

Diagnosis	Pulm Blood Flow	CXR Heart	CXR Lungs	Characteristic ECG	Characteristic Murmur	Duct Dependent
PAIVS	↓	Variable	Oligaemic	LV dominance	PSM (TR) + PDA	√
PAVSD	↓	Boot-shaped	Oligaemic/uneven	RAD, RVH	No PS; ± MAPCA continuous	√
TOF	↓	Boot-shaped	Oligaemic	RAD, RVH	ESM at LUSB (PS)	±
Tricuspid Atresia	↓	Variable	Oligaemic	LAD (superior axis)	Variable	±
Ebstein's	↓	Massive cardiomegaly	Oligaemic	Tall P, RBBB, ± WPW	PSM (TR)	±
Critical PS	↓	Variable	Oligaemic	LV dominance (similar to PAIVS)	ESM at LUSB (faint)	√
TGA	↑	Egg on string	Plethoric	RVH	Usually soft/absent	√
Truncus Arteriosus	↑	Cardiomegaly	Plethoric	Biventricular hypertrophy	Systolic ejection click	✗
TAPVR	↑	Snowman (supracardiac)	Plethoric or oedema	RAD, RVH	Fixed split S2	✗

High Yield Summary — DDx of Pulmonary Atresia

First distinguish cardiac from non-cardiac cyanosis: hyperoxia test (PaO₂ < 100–150 on 100% FiO₂ = cardiac); oligaemic lung fields on CXR support cardiac cause ^[4]
PPHN mimics cyanotic CHD — differentiate by Echo showing structurally normal heart
Categorise cyanotic CHD by pulmonary blood flow ^[5]: ↓ pulmonary flow (oligaemic) vs ↑ flow (plethoric) vs severe HF
PA sits in the ↓ pulmonary blood flow group alongside TOF, tricuspid atresia, critical PS, and Ebstein's
PAVSD vs TOF: no PS murmur in PA (no flow = no murmur); PAVSD is the extreme end of the TOF spectrum ^[1]
PAIVS vs PAVSD: intact septum, hypoplastic RV, LV dominance on ECG, PSM from TR (PAIVS) vs VSD present, RVH on ECG, ± MAPCAs (PAVSD)
PAIVS vs Critical PS: nearly identical clinically; Echo shows no antegrade PV flow in PAIVS vs tiny jet in critical PS; critical PS is amenable to balloon valvuloplasty ^[7]
Tricuspid atresia: classic LAD on ECG (vs LV dominance without LAD in PAIVS)
Ebstein's: massive cardiomegaly disproportionate to symptoms; WPW on ECG in ~20%
Always check for syndromes: 22q11.2 (PAVSD), Noonan (dysplastic PS), Alagille (peripheral PS)

Active Recall - Differential Diagnosis of Pulmonary Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 215–217) ^[3] Senior notes: Ryan Ho Cardiology.pdf (pages 185–189) ^[4] AOS material: AOS - Paeds.pdf (Question 6) ^[5] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (page 280) ^[6] Senior notes: Maksim Paediatric Notes.pdf (pages 55–56) ^[7] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (pages 284–285)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Pulmonary Atresia

Pulmonary atresia does not have a formal "diagnostic criteria" set like rheumatic fever (Jones criteria) or Kawasaki disease. Instead, it is a morphological/anatomical diagnosis confirmed by imaging. The diagnosis requires demonstration of:

Complete absence of antegrade flow from the RV to the pulmonary arteries (i.e., an atretic pulmonary valve or completely obliterated RVOT)
Classification into PAIVS or PAVSD based on the presence or absence of a ventricular septal defect
Delineation of the source of pulmonary blood flow (PDA, MAPCAs, or both)

However, before imaging confirms the anatomy, the clinician must go through a structured clinical recognition pathway for duct-dependent cyanotic heart disease. This is the practically important "diagnostic approach" for exams and clinical care.

The diagnostic process unfolds in four phases:

Phase	Goal	Key Tools
1. Recognition	Identify that the neonate is cyanotic and that this is not normal	Pulse oximetry screening, clinical observation
2. Differentiation	Cardiac vs non-cardiac cause	Hyperoxia test, CXR, pre/post-ductal SpO₂
3. Anatomical diagnosis	Define the specific cardiac lesion	Echocardiography (primary), ± ECG
4. Detailed delineation	Map pulmonary blood supply, coronary anatomy, suitability for repair	CT angiography / cardiac MRI / cardiac catheterisation

Universal newborn pulse oximetry screening is now standard practice in Hong Kong (and most developed countries) to detect critical congenital heart disease (CCHD) before ductal closure leads to collapse ^[8].

Protocol (as per AAP/HK recommendations):

Performed at 24–48 hours of life (or before discharge if earlier)
Measure SpO₂ on the right hand (pre-ductal) and either foot (post-ductal)
Positive screen (requires further evaluation):
- Any SpO₂ reading < 90% in either limb → immediate echocardiography
- SpO₂ 90–94% in both limbs OR > 3% difference between pre- and post-ductal → repeat in 1 hour; if still abnormal after 3 measurements → echocardiography
- SpO₂ ≥ 95% in either limb AND ≤ 3% difference → pass (negative screen)

Why right hand specifically? The right hand is supplied by the right subclavian artery, which arises from the brachiocephalic trunk — proximal to the ductus arteriosus. This gives pre-ductal saturation (blood that has not yet mixed with ductal flow). The feet receive post-ductal blood. A pre/post-ductal difference suggests either differential shunting (as in PPHN or coarctation) or ductal-level mixing.

Clinical Pearl — PA and Pulse Oximetry

In pulmonary atresia, SpO₂ is low in both pre-ductal and post-ductal sites because the mixing occurs at the atrial level (PAIVS) or ventricular level (PAVSD), proximal to the ductus. The pre/post-ductal gradient is typically small or absent (unlike coarctation or PPHN where the gradient is prominent). However, any reading < 90% triggers immediate investigation.

Phase 2: Differentiation — Cardiac vs Non-Cardiac Cyanosis

This is the bedside screening test to distinguish cardiac from pulmonary causes of cyanosis.

Method:

Obtain a baseline arterial blood gas (ABG) on room air (right radial artery = pre-ductal)
Place the neonate on 100% FiO₂ via head box or non-rebreather mask for 10–15 minutes
Repeat the ABG

Interpretation:

PaO₂ on 100% FiO₂	Interpretation	Mechanism
> 200 mmHg	Normal / Pulmonary disease (responds to O₂)	Supplemental O₂ overcomes V/Q mismatch or diffusion impairment
150–200 mmHg	Possible cardiac lesion with some pulmonary flow OR significant lung disease	Incomplete mixing or moderate shunt
< 100–150 mmHg	Strongly suggestive of cyanotic CHD (fixed R→L shunt)	No amount of supplemental O₂ can oxygenate blood that bypasses the lungs via an R→L intracardiac shunt
< 50 mmHg	Almost certainly cyanotic CHD OR severe PPHN	Profound fixed shunt — virtually no blood passing through pulmonary capillaries

Why doesn't O₂ work in cyanotic CHD? In pulmonary atresia, the deoxygenated blood bypasses the lungs entirely (via PFO in PAIVS, via VSD in PAVSD). Increasing the FiO₂ only affects the small amount of blood that does reach the alveoli (via PDA). The majority of blood is shunted and never sees the alveolar O₂. This is a fixed right-to-left shunt — supplemental O₂ cannot improve it because the problem is anatomical, not ventilation-related.

Exam Trap

Do NOT delay prostaglandin E1 while waiting for the hyperoxia test result in a critically cyanotic neonate. If clinical suspicion of duct-dependent CHD is high (cyanosis unresponsive to O₂, oligaemic lung fields), start PGE1 immediately and investigate in parallel. The hyperoxia test is a diagnostic aid, not a prerequisite for treatment.

Pattern	Likely Cause
Both low, minimal gradient	Intracardiac mixing lesion (PA, TGA, etc.)
Pre-ductal higher than post-ductal ( > 3% difference)	PPHN, interrupted aortic arch, critical coarctation
Post-ductal higher than pre-ductal (reverse differential)	TGA with coarctation (rare)

The CXR provides three crucial pieces of information:

Heart size and shape — cardiomegaly? Specific silhouettes?
Pulmonary vascular markings — oligaemic or plethoric?
Lung parenchyma — clear (cardiac) or diseased (respiratory)?

"Radiograph showing an oligaemic lung field due to reduced pulmonary blood flow SUPPORTS cyanotic congenital heart disease rather than respiratory disease" ^[4]

Echocardiography is the definitive diagnostic tool for confirming the anatomical diagnosis of pulmonary atresia. It is non-invasive, radiation-free, portable (can be done at the bedside in NICU), and provides real-time structural and haemodynamic information.

Investigation Modalities — Detailed Findings and Interpretation

1. Chest X-Ray (CXR)

Finding	Interpretation/Pathophysiological Basis
Heart size normal or enlarged	Variable — depends on degree of TR and RA dilation
Grossly enlarged RA/RV due to TR	Severe tricuspid regurgitation → massive RA dilation; the RV itself is thick-walled but small-cavitied, but the RA balloons out
Diminished pulmonary vascular markings	Duct-dependent pulmonary circulation — reduced pulmonary blood flow because the only source is the PDA, which is constricting

Why can the heart be massively enlarged in PAIVS? In cases with severe TR, the blood regurgitates back and forth between the RV and RA with each cardiac cycle. The RA progressively dilates. In extreme cases (similar to Ebstein's anomaly), the heart silhouette can become very large despite the lung fields being oligaemic — a combination of big heart + dark lungs.

Finding	Interpretation/Pathophysiological Basis
Boot-shaped heart (coeur en sabot)	Upturned apex from RV hypertrophy + concave main PA segment (absent/hypoplastic PA) — identical to TOF
Oligaemic lung fields	Reduced pulmonary blood flow (if PDA constricting and MAPCAs stenosed/inadequate)
Uneven pulmonary vascularity depending on course, site, size of collaterals	Different lung segments supplied by different MAPCAs of varying calibre → some segments well-perfused, others not → asymmetric vascular markings

Why "boot-shaped"? The normal cardiac silhouette has a gentle concavity at the left heart border where the main pulmonary artery segment sits. In TOF/PAVSD, the main PA is hypoplastic or absent → this concavity becomes exaggerated. Combined with the upturned apex from RVH, the heart looks like a boot (or a wooden clog).

CXR Comparison Across Cyanotic CHD

Diagnosis	CXR Heart Shape	CXR Lung Fields
PAIVS	Variable, may be massive (if severe TR)	Oligaemic
PAVSD	Boot-shaped	Oligaemic or uneven
TOF	Boot-shaped	Oligaemic
TGA	"Egg on a string" (narrow mediastinum)	Plethoric
TAPVR (supracardiac)	"Snowman" / figure-of-eight	Plethoric or oedematous
Ebstein's	Massive cardiomegaly ("wall-to-wall")	Oligaemic
Tricuspid Atresia	Variable (often small heart)	Oligaemic

2. Electrocardiogram (ECG)

The ECG in neonates must be interpreted with age-appropriate normal values in mind. In the normal neonate, RV dominance is expected (the fetal RV does ~60% of cardiac output against the high-resistance placental/pulmonary circuit). This dominance gradually shifts to LV dominance over the first months of life.

Finding	Interpretation/Pathophysiological Basis
RA dilation (P pulmonale)	Peaked P waves in lead II ( > 3 mm in neonates) — RA volume and pressure overload from TR and obligatory R→L shunting; the RA is working hard to decompress
LV dominance with paucity of RV forces	The RV is hypoplastic with minimal muscle mass → generates very little electrical activity. The LV does all the cardiac work (supplies both systemic and pulmonary circuits) → dominant LV forces. This is abnormal for a neonate, where RV dominance is expected ^[1]

Why is LV dominance in a neonate alarming? Normally, a neonate's ECG shows RV dominance (dominant R wave in V1, right axis deviation) because the fetal RV was the dominant ventricle. Finding LV dominance (dominant R in V5–V6, dominant S in V1) in a neonate suggests either:

RV hypoplasia (as in PAIVS)
LV volume overload from a large L→R shunt (but these neonates are acyanotic)
Tricuspid atresia (absent RV)

In the context of a cyanotic neonate, LV dominance on ECG + cyanosis = think PAIVS or tricuspid atresia.

Finding	Interpretation/Pathophysiological Basis
Right axis deviation (RAD)	RV hypertrophy → rightward electrical axis
RVH	Tall R waves in V1, deep S waves in V5–V6; the RV is well-developed and hypertrophied (ejects blood at systemic pressure through VSD into aorta, similar to TOF)

Why is the ECG pattern different between PAIVS and PAVSD? This is a frequently tested point:

PAIVS: RV has no outlet (blind-ending chamber), becomes hypertrophied but hypoplastic (thick walls, tiny cavity) → generates minimal electrical forces → paucity of RV forces, LV dominance ^[1]
PAVSD: RV has an outlet (VSD → aorta), continues to eject blood against systemic resistance → RV is well-developed and hypertrophied → RVH on ECG ^[1]

The difference boils down to whether the RV has a functional outlet or not. If it can eject blood (even through a VSD), it develops muscle mass and generates ECG voltage. If it is a dead-end chamber, it generates almost nothing.

3. Echocardiography — The Definitive Diagnostic Tool

Echocardiography is the gold standard for the initial anatomical diagnosis of pulmonary atresia. It should be performed urgently in any neonate with suspected cyanotic CHD.

Finding	Technique/View	Interpretation
Delineate type of pulmonary atresia: valvular vs infundibular	Parasternal short-axis view; subcostal views	Imperforate valve membrane (valvular) vs complete muscular obliteration (infundibular) — valvular type may be amenable to perforation/balloon valvuloplasty
Delineate degree of RV hypoplasia	4-chamber view; tricuspid valve annulus Z-score	Tripartite (inlet + trabecular + infundibular) vs bipartite vs unipartite RV; TV annulus Z-score predicts suitability for biventricular repair
Detect abnormal Rt ventriculo-coronary sinusoidal flow	Colour Doppler from RV cavity	Retrograde flow from RV into coronary arteries — critical to identify because it determines whether RVDCC is present and whether the RV can be decompressed ^[1]
Assess PFO/ASD size and direction of shunt	Subcostal view with colour Doppler	Obligatory R→L shunt; restrictive PFO → severely elevated RA pressure → poor cardiac output
PDA size and flow	Suprasternal or high parasternal view	Sole source of pulmonary blood flow — assess adequacy
Tricuspid valve size (Z-score) and degree of regurgitation	4-chamber view	Small and incompetent ^[1]; TV Z-score < −2 to −4 indicates significant hypoplasia; TR jet velocity estimates RV pressure

Understanding Z-scores in paediatric echocardiography: A Z-score expresses how many standard deviations a measurement is from the mean for that body surface area (BSA). For example:

TV annulus Z-score of 0 = average for size
Z-score of −2 = 2 SD below mean = small
Z-score of −4 = profoundly hypoplastic

In PAIVS, the TV annulus Z-score is one of the most important prognostic measurements — it correlates with RV cavity size and determines whether a biventricular repair (connecting RV to PA) is feasible or whether the patient must go down a single-ventricle (Fontan) pathway.

Finding	Technique/View	Interpretation
Atretic RV outflow with RVH and VSD	Parasternal long-axis, short-axis views	Confirms the diagnosis — no continuity between RV and PA; large malalignment VSD with overriding aorta
Native pulmonary artery confluence and size	Suprasternal view	Confluent native PAs (even if hypoplastic) are prognostically favourable — can be grown with staged surgery; absent native PAs → MAPCA-dependent
Aortopulmonary collateral flow	Suprasternal, high parasternal views	Colour Doppler may detect collateral flow, but detailed delineation only by MRI, cardiac catheterisation ^[1] — echo alone cannot fully map MAPCAs
PDA size and direction	Suprasternal view	Assess whether PDA is the primary source or supplementary to MAPCAs
Right-sided aortic arch	Suprasternal view	Present in 50% of PAVSD ^[1] — the aortic arch goes rightward instead of leftward

Echo Cannot Fully Map MAPCAs

"Aortopulmonary collateral flow → detailed delineation only by MRI, cardiac catheterisation" ^[1]. This is a critical point: while Echo can confirm the intracardiac anatomy (atretic RVOT, VSD, overriding aorta), it cannot reliably map all the MAPCAs because these arise from the descending aorta (which is difficult to image by transthoracic echo in neonates). Cross-sectional imaging (CT angiography or cardiac MRI) and/or diagnostic cardiac catheterisation are needed for complete preoperative planning.

Role: Detailed 3D anatomical mapping, especially for PAVSD with MAPCAs.

What CTA Shows	Clinical Relevance
Native PA size and confluence	Determines if unifocalisation is possible
Number, origin, course, and calibre of each MAPCA	Essential for surgical planning of unifocalisation
Which lung segments are supplied by native PAs vs MAPCAs (dual supply vs single supply)	Segments with only MAPCA supply cannot lose that collateral until native PA supply is established
Airway anatomy	Rules out associated tracheobronchomalacia or vascular rings

Advantages over catheterisation: Non-invasive, faster, excellent spatial resolution, 3D reconstruction. Disadvantages: Radiation exposure (significant concern in neonates), requires contrast, provides no haemodynamic data (pressures, resistances).

In current practice (2025–2026): CTA has largely replaced diagnostic catheterisation as the first-line cross-sectional imaging for PAVSD anatomy. Catheterisation is reserved for when haemodynamic data are needed or when intervention is planned.

Role: Alternative to CTA; particularly useful for follow-up imaging (no radiation).

What MRI Shows	Clinical Relevance
RV volume and function	Quantitative assessment of RV size (critical for PAIVS: can the RV sustain biventricular circulation?)
Native PA anatomy	Confluence, size, stenoses
MAPCA mapping	Similar to CTA but without radiation
Flow quantification	Can measure Qp:Qs ratio and differential lung perfusion

Advantages: No radiation, excellent soft tissue contrast, functional data. Disadvantages: Requires sedation/general anaesthesia in neonates and infants (long scan times), limited availability, not ideal in critically ill unstable neonates.

6. Cardiac Catheterisation

Role: Historically the gold standard for complete anatomical and haemodynamic assessment. Now increasingly reserved for therapeutic intervention and selected diagnostic situations where non-invasive imaging is insufficient.

Data	Clinical Relevance
Haemodynamic measurements	RV pressure (suprasystemic in PAIVS?), PA pressures, pulmonary vascular resistance (PVR) — critical for surgical planning
Angiography of MAPCAs	Definitive mapping of all collaterals — their origin, calibre, and which lung segments they supply
RV angiography	Demonstrates ventriculo-coronary sinusoidal communications and RVDCC in PAIVS — this is the gold standard for detecting RVDCC
Coronary angiography	Identifies coronary stenoses proximal to sinusoidal connections — determines if decompressing the RV is safe
Aortography	Maps all sources of pulmonary blood flow from the aorta

Procedure	Indication
Balloon atrial septostomy (Rashkind procedure)	Enlarge restrictive PFO in PAIVS → decompress RA → improve cardiac output
PDA stenting	Maintain pulmonary blood flow as alternative to surgical BT shunt
Pulmonary valve perforation + balloon valvuloplasty	In critical PS (not true PAIVS) — converts a membranous atresia to a patent valve; also sometimes attempted in PAIVS with favourable anatomy
MAPCA coil embolisation	Occlude redundant MAPCAs that are causing pulmonary overcirculation

Finding	Interpretation
Low PaO₂ (typically 25–45 mmHg on room air)	Fixed R→L shunt — blood bypassing lungs
Metabolic acidosis (↓pH, ↓HCO₃⁻, ↑lactate)	Tissue hypoxia → anaerobic metabolism → lactic acidosis; ominous sign indicating inadequate oxygen delivery
Normal or low PaCO₂	Tachypnoea → respiratory alkalosis (compensatory); if PaCO₂ is elevated → superimposed respiratory failure or exhaustion

Investigation	Rationale
Complete blood count (CBC)	Polycythaemia may develop in chronic cyanosis (compensatory erythropoietin response); also baseline for surgical planning
Serum calcium, ionised calcium	Screen for hypocalcaemia → 22q11.2 deletion (DiGeorge), especially in PAVSD
Genetic testing (FISH / chromosomal microarray for 22q11.2)	Indicated in PAVSD ± MAPCAs; DiGeorge is the most common associated syndrome
Renal ultrasound	Screen for renal anomalies (associated in some syndromic cases)
Brain imaging	If seizures or neurological concerns from hypoxic episodes

Investigation	PAIVS Key Findings	PAVSD Key Findings
CXR	Normal/enlarged heart; RA dilation (TR); diminished PVM ^[1]	Boot-shaped heart; oligaemic or uneven PVM ^[1]
ECG	P pulmonale; LV dominance; paucity of RV forces ^[1]	RAD; RVH ^[1]
Echo	Valvular vs infundibular atresia; RV hypoplasia degree; ventriculo-coronary sinusoidal flow ^[1]	Atretic RVOT with VSD; collateral flow; native PA confluence ^[1]
CTA / MRI	RV volume; coronary anatomy	MAPCA mapping (detailed delineation) ^[1]
Catheterisation	Gold standard for RVDCC; RV pressure; coronary angiography	MAPCA angiography; haemodynamic data; potential intervention
ABG	Low PaO₂; metabolic acidosis if deteriorating	Low PaO₂; metabolic acidosis if deteriorating
Genetics	Not routinely indicated (sporadic)	22q11.2 FISH/microarray (especially with MAPCAs)

High Yield Summary — Investigations in Pulmonary Atresia

Pulse oximetry screening at 24–48h of life detects CCHD before ductal closure; SpO₂ < 90% → immediate evaluation
Hyperoxia test: PaO₂ < 100–150 mmHg on 100% FiO₂ = fixed R→L shunt = cardiac cause; do not delay PGE1 for this test
CXR in PAIVS: variable heart size ± massive RA; diminished pulmonary vascular markings ^[1]
CXR in PAVSD: boot-shaped heart; oligaemic or uneven lung fields ^[1]
"Oligaemic lung field supports cyanotic CHD over respiratory disease" ^[4]
ECG — the key differentiator: PAIVS = LV dominance (abnormal for a neonate); PAVSD = RAD + RVH ^[1]
Echo is the definitive diagnostic tool: confirms anatomy, assesses RV size (TV Z-score), detects ventriculo-coronary sinusoidal flow ^[1]
MAPCAs cannot be fully mapped by Echo → detailed delineation only by MRI or cardiac catheterisation ^[1]
Cardiac catheterisation is the gold standard for detecting RVDCC in PAIVS — determines whether biventricular repair is safe
22q11.2 genetic testing is mandatory in PAVSD, especially with MAPCAs

Active Recall - Diagnostic Criteria, Algorithm, and Investigations for Pulmonary Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 215–222) ^[4] AOS material: AOS - Paeds.pdf (Question 6) ^[8] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf

Management of Pulmonary Atresia

The management of pulmonary atresia follows a staged approach that reflects the severity and urgency of the physiology. Think of it in three time-frames:

Emergency stabilisation (minutes to hours) — keep the baby alive
Initial palliation (days to weeks) — establish reliable pulmonary blood flow
Definitive repair or palliation (months to years) — biventricular repair if anatomy permits, or single-ventricle (Fontan) pathway if not

The management strategy differs fundamentally between PAIVS and PAVSD because the anatomy, RV potential, and coronary issues are different. We will cover each in turn.

Phase 1: Emergency Stabilisation (Neonatal Period)

This applies to both PAIVS and PAVSD — they are both duct-dependent lesions.

Emergency IV PGE1 infusion to maintain ductal patency ^[1]

Rationale from first principles: The ductus arteriosus is the sole (PAIVS) or major (PAVSD) source of pulmonary blood flow. After birth, rising PaO₂ and falling circulating PGE₂ (which was maintained by the placenta) trigger ductal constriction. PGE1 (alprostadil) is a synthetic prostaglandin E₁ analogue that acts on smooth muscle prostaglandin receptors in the ductal wall to keep it dilated.

PGE1 Details	Notes
Drug	Alprostadil (Prostin VR)
Route	IV infusion — via peripheral or umbilical venous catheter
Starting dose	0.01–0.05 mcg/kg/min
Maintenance dose	Often titrated down to 0.01–0.02 mcg/kg/min once duct is open (to minimise side effects)
Onset	Within minutes to hours
Monitoring	Continuous SpO₂, heart rate, blood pressure; watch for response (↑SpO₂, improved perfusion)

Side effects of PGE1 in neonates — must know:

Side Effect	Mechanism	Clinical Implication
Apnoea	PGE1 acts on brainstem respiratory centres → central apnoea	Have intubation equipment and ventilatory support ready; some centres electively intubate before PGE1 in very sick neonates
Fever	Prostaglandin-mediated thermoregulatory reset	Common, usually mild; may confuse with sepsis evaluation
Hypotension	Vasodilatory effect of prostaglandins on systemic vasculature	Monitor BP closely; may need volume support
Diarrhoea	PGE1 stimulates intestinal secretion and motility	Usually manageable
Seizure-like activity	Rare; mechanism unclear	Report if occurs
Cortical hyperostosis	Long-term side effect (weeks of use) — periosteal new bone formation	Relevant if prolonged use before surgery

Exam Must-Know: PGE1 Side Effects

"PGE1 side effects: fever, apnoea, diarrhoea" ^[6]. Apnoea is the most dangerous and the reason neonates on PGE1 must be in a unit with ventilatory capability. The mnemonic "FAD" — Fever, Apnoea, Diarrhoea — captures the key ones.

Measure	Rationale
Oxygen	Use with caution — in duct-dependent lesions, supplemental O₂ can paradoxically worsen the situation by promoting ductal constriction (O₂ is one of the stimuli for ductal closure); target SpO₂ ~75–85% in mixing lesions, not 100%
Correct metabolic acidosis	NaHCO₃ if pH < 7.1 and not responding to improved perfusion; ensure adequate ventilation first
Volume resuscitation	10 mL/kg NS bolus if signs of poor perfusion; avoid over-hydration
Intubation and ventilation	If apnoeic (PGE1 side effect), or in cardiogenic shock
Inotropes	Dopamine or dobutamine if cardiogenic shock despite PGE1 and volume
Avoid excessive stimulation	Minimise handling — crying and agitation increase O₂ consumption and can worsen cyanosis

"± balloon atrial septostomy to ↑ mixing" ^[1]

Indication in PAIVS: If the PFO/ASD is restrictive (small), the RA cannot adequately decompress through it → severely elevated RA pressure → poor cardiac output. Balloon atrial septostomy creates a larger interatrial communication to allow better R→L shunting and decompress the RA.

Procedure: A balloon-tipped catheter is advanced via the femoral vein or umbilical vein into the RA → through the PFO → into the LA. The balloon is inflated and pulled back forcefully through the atrial septum → tears it open.

This is done at the bedside under echocardiographic guidance in the NICU — no need to transfer to the catheterisation lab.

Not routinely needed in PAVSD — because in PAVSD, the blood exits the RV through the VSD (not through the atrial septum), so atrial septostomy is less relevant.

Phase 2: Initial Palliation — Establishing Reliable Pulmonary Blood Flow

Once the baby is stabilised on PGE1, the PDA must be replaced with a more reliable and permanent source of pulmonary blood flow because PGE1 cannot be continued indefinitely. There are two main palliative options:

This is the most commonly used palliative procedure for duct-dependent cyanotic heart disease ^[1]^[3].

"Modified Blalock-Taussig shunt — provide extra pulmonary flow for cyanotic heart disease with inadequate pulmonary flow or in frank duct-dependent pulmonary circulation" ^[1]

What it is: A synthetic Gore-Tex graft (typically 3.0–4.0 mm diameter in neonates) is placed between the subclavian or innominate artery and the ipsilateral pulmonary artery, creating a systemic-to-pulmonary shunt that provides continuous pulmonary blood flow ^[3].

Why "modified"? The original Blalock-Taussig shunt (described by Alfred Blalock and Vivien Thomas in 1944) involved directly anastomosing the subclavian artery to the PA, which sacrificed the subclavian artery. The modified version interposes a synthetic graft, preserving the subclavian artery and its distal flow.

Feature	Details
Graft size	Typically 3.0–3.5 mm for neonates; 4.0 mm for larger infants
Side	Usually right-sided (right subclavian/innominate to right PA)
Effect	Creates a continuous L→R shunt → ↑ pulmonary blood flow → ↑ oxygenation
Murmur	Continuous murmur under the clavicle — always listen for shunt murmur on follow-up; blocked B-T shunt can kill ^[3]

Indications for mBTS ^[1]:

Pre-repair TOF with severe cyanosis or uncontrolled Tet spell
PAVSD with duct dependence
PAIVS before Fontan operation
Univentricular heart with inadequate pulmonary flow

Complications of mBTS:

Shunt thrombosis — most feared complication; presents with acute cyanosis, loss of shunt murmur → medical emergency → may need urgent re-operation or catheter intervention
Shunt overflow — excessive pulmonary blood flow → heart failure, pulmonary hypertension (shunt too big)
Distortion of pulmonary artery — the graft can kink or distort the PA at the anastomotic site
Chylothorax — from surgical dissection near the thoracic duct

Life-Threatening Complication — Blocked BT Shunt

"Always listen for shunt murmur on F/U → blocked B-T shunt can kill" ^[3]. A child with an mBTS who suddenly becomes deeply cyanotic and whose continuous murmur disappears has a blocked shunt until proven otherwise. This requires immediate heparinisation, fluid resuscitation, and urgent surgical or catheter intervention. Low-dose aspirin (3–5 mg/kg/day) is typically prescribed post-mBTS to prevent thrombosis.

What it is: A metallic stent is deployed within the ductus arteriosus via cardiac catheterisation to keep it open, as an alternative to surgical mBTS.

Feature	Details
Approach	Femoral venous or arterial access → catheter advanced to the ductus → stent deployed
Advantage	Avoids sternotomy/thoracotomy in a fragile neonate; less invasive
Disadvantage	Duct anatomy can be tortuous (may be technically difficult); stent may become stenosed over time; may distort PA
Current role	Increasingly used as an alternative to mBTS in selected centres, particularly in lower-weight neonates or those with unfavourable surgical anatomy

Pulmonary arterial banding ^[1] is used in the opposite clinical scenario — when pulmonary blood flow is excessive (e.g., PAVSD with unrestricted MAPCAs causing heart failure and pulmonary hypertension).

Feature	Details
What it does	A band (a strip of synthetic material) is placed around the main pulmonary artery → constricts it → restricts excessive pulmonary blood flow
Indication	Heart failure from excessive pulmonary flow — i.e., PAVSD with unrestricted MAPCAs; some univentricular hearts without pulmonary stenosis
Paradox	In PA, banding is rarely applied to the main PA (which is atretic), but individual MAPCAs may need to be surgically or catheter-controlled

This is where PAIVS and PAVSD diverge completely.

PAIVS — Definitive Management

Definitive repair depends on size/function of RV and coronary anatomy ^[1]

The critical decision tree in PAIVS is:

Is the RV adequate for biventricular repair? (assessed by TV Z-score, RV morphology — tripartite vs bipartite vs unipartite)
Is there RV-dependent coronary circulation (RVDCC)? (assessed by cardiac catheterisation)

A. Biventricular Repair (if RV adequate and no RVDCC)

"Adequate RV size and function with no RVDCC" ^[1]

The goal is to establish antegrade flow from the RV to the pulmonary artery, decompress the RV, and promote RV growth.

"Valvar atresia → transcatheter laser- or RFA-assisted pulmonary valvotomy followed by balloon valvuloplasty or surgical pulmonary valvotomy" ^[1]

Procedure	Mechanism
Transcatheter pulmonary valve perforation	A wire or radiofrequency (RFA) probe is advanced from the RV to perforate the atretic valve membrane, creating a small opening
Followed by balloon valvuloplasty	A balloon catheter is inflated across the newly created opening to enlarge it — this re-establishes antegrade flow from RV to PA
Alternative: Surgical pulmonary valvotomy	Open-heart incision of the atretic valve — used if catheter approach is technically not feasible

"Infundibular atresia → surgical RVOT reconstruction" ^[1]

This requires open-heart surgery to create a new outflow tract from the RV to the PA, often using a patch (transannular or non-transannular) or an RV-PA conduit.

"± post-op palliative shunting (stenting of PDA or modified B-T shunt) as RV function may still be poor → provide adequate pulmonary flow" ^[1]

Even after RV decompression, the RV is often too small and stiff to generate adequate pulmonary blood flow immediately. A temporary shunt provides supplementary pulmonary flow while the RV grows and remodels.

"Shunting only to tide over the period → can be catheter occluded later after good RV growth" ^[1]

As the RV grows and assumes more of the pulmonary circulation workload, the shunt becomes redundant and can be closed (surgically or by catheter device occlusion).

Indications for univentricular palliation ^[1]:

Severely hypoplastic RV: cannot support the pulmonary circulation
RV-dependent coronary circulation (RVDCC): RVOT reconstruction is contraindicated as it results in ↓RV pressure → coronary steal → myocardial ischaemia ^[1]

Why RVDCC Precludes Biventricular Repair — From First Principles

In RVDCC, the coronary arteries depend on the suprasystemic RV pressure to perfuse them (because of proximal coronary stenosis + sinusoidal connections). If you decompress the RV (by opening the RVOT), the RV pressure drops to subpulmonary levels. The coronary arteries, now without their high-pressure retrograde supply and with proximal stenosis blocking antegrade aortic flow, become ischaemic. This leads to myocardial infarction and death. Therefore, the RV pressure must be maintained high → the patient cannot have a biventricular repair and must go down the Fontan pathway where the RV pressure remains high (as it is excluded from the pulmonary circuit).

The Staged Fontan Pathway

The Fontan pathway is a staged surgical sequence that ultimately separates the systemic and pulmonary circulations by routing systemic venous blood directly to the pulmonary arteries without a subpulmonary ventricle.

Stage	Procedure	Timing	What It Does
Stage 1	Modified BT shunt or PDA stent	Neonatal period	Provides pulmonary blood flow; replaces the PDA
Stage 2	Bidirectional Glenn (cavopulmonary anastomosis)	4–6 months	SVC is disconnected from RA and anastomosed directly to the right PA → SVC blood flows directly to lungs without passing through a ventricle; mBTS is taken down
Stage 3	Fontan completion (total cavopulmonary connection)	2–4 years	IVC blood is also routed directly to the PA (via an intracardiac lateral tunnel or extracardiac conduit) → all systemic venous blood now flows passively to lungs

Why staged? You cannot do a Fontan in a neonate because:

Neonatal PVR is still too high to allow passive venous flow through the lungs
The PA must be of adequate size to accept the full systemic venous return without a pump
Each stage allows the pulmonary vasculature to remodel and the PAs to grow

Result of completed Fontan: The single ventricle (LV) serves as the sole systemic pump. All systemic venous blood flows passively through the lungs driven only by the central venous pressure gradient. Oxygen saturations typically reach 90–95% (not 100%, because of small fenestrations or bronchial venous drainage).

For patients with borderline RV size — not adequate for full biventricular repair but not so hypoplastic as to require Fontan:

Procedure	What It Does
Bidirectional Glenn + RV decompression	SVC blood goes directly to PA (Glenn); IVC blood returns to RA → crosses into RV → is pumped to PA by the small RV. The RV only needs to handle half the venous return (IVC only), which a borderline RV can manage

This is called a "1.5-ventricle repair" because the RV handles approximately half the cardiac output (IVC return only), and the SVC return bypasses the heart entirely.

PAVSD — Definitive Management

The management of PAVSD is complex because it requires not only repairing the intracardiac anatomy but also establishing a reliable, unified pulmonary arterial blood supply from the multiple MAPCAs.

Unifocalisation is a surgical procedure unique to PAVSD with MAPCAs. It involves:

Disconnecting each MAPCA from the aorta
Connecting (anastomosing) all the MAPCAs together and to the native pulmonary arteries (if present) to create a single, unified pulmonary arterial tree
Once all lung segments are connected to this unified tree, the tree is connected to the RV via an RV-PA conduit
The VSD is closed so that the RV only pumps to the lungs (not to the aorta)

Why can't you just close the VSD immediately? If you close the VSD before the PA tree is adequate (too small, too high resistance), the RV will be pumping against high resistance with no "pop-off" valve → RV failure → death. The VSD must remain open until the PA tree is large enough and the PVR is low enough to accept the full RV output.

Feature	Details
What	A tube (homograft or synthetic) placed between the RV and the main PA/unifocalised PA tree
Why	The native RVOT is atretic — a conduit bypasses this obstruction
Material	Pulmonary or aortic homograft (most common); bovine jugular vein (Contegra); synthetic (less common)
Long-term issue	Conduit degeneration — homografts calcify and stenose over time; virtually all patients will need conduit replacement at least once during childhood/adolescence; typical lifespan of a conduit is 5–15 years

Management summary from lecture notes — "Blalock-Taussig shunt: major systemic artery is shunted to the newly unifocalised pulmonary arterial tree" ^[7]

While the definitive treatment of PA is surgical/interventional, medical management plays a supportive role:

Intervention	Role	Paediatric Considerations
Anti-failure medications	For those with HF from excess pulmonary flow (PAVSD with unrestricted MAPCAs)	Diuretics (furosemide 1–2 mg/kg/dose; spironolactone 1–2 mg/kg/day); avoid ACEI/ARB in single-ventricle physiology with R→L shunt — ↓SVR → ↑R→L shunting → worsened cyanosis (same principle as TOF ^[3])
Antiplatelet therapy	Post-mBTS to prevent shunt thrombosis	Low-dose aspirin 3–5 mg/kg/day
Iron supplementation	Chronic cyanosis → compensatory polycythaemia → high iron demand	Relative iron deficiency can cause hyperviscosity symptoms even without absolute anaemia
Antibiotic prophylaxis (IE)	All patients with PA (repaired or unrepaired) are at high risk of infective endocarditis	Amoxicillin 50 mg/kg (max 2g) 30–60 min before dental procedures; lifelong in those with residual lesions, prosthetic material, or conduits
Nutritional support	↑ metabolic demand + poor feeding → failure to thrive	High-calorie feeds (breast milk fortifier or high-calorie formula); consider NG tube feeds if inadequate oral intake
Fluid restriction	If significant HF	Typically 100–120 mL/kg/day in infants with HF (rather than normal 150 mL/kg/day)

Why Avoid ACEI in Duct-Dependent / R→L Shunt Lesions?

ACE inhibitors and ARBs cause systemic vasodilation (↓SVR). In a child with a R→L shunt (as in PA), lowering SVR means more blood preferentially shunts right-to-left (away from the lungs) rather than into the systemic circulation. This worsens cyanosis. This is the same principle as why ↓SVR triggers Tet spells in TOF ^[3]. Diuretics (which ↓preload, not ↓SVR) are the safer anti-failure option.

All patients with pulmonary atresia — whether they underwent biventricular repair, 1.5-ventricle repair, or Fontan — require lifelong cardiac follow-up. This is a core principle of grown-up congenital heart disease (GUCH) care.

Issue	Monitoring/Management
Conduit stenosis/degeneration (PAVSD)	Serial echo ± MRI; conduit replacement when significant obstruction (RV pressure > 2/3 systemic) or symptoms
Pulmonary regurgitation (after RVOT reconstruction)	Same principle as post-TOF repair: RV dilation → dysfunction → arrhythmia → sudden death; monitor with MRI (RV volumes, regurgitant fraction); PV replacement when criteria met ^[3]
Fontan complications (if univentricular pathway)	Fontan failure (low cardiac output, exercise intolerance), protein-losing enteropathy, plastic bronchitis, Fontan-associated liver disease, thromboembolic events, arrhythmias
Arrhythmias	Late-onset atrial flutter/fibrillation, ventricular tachycardia (especially after ventriculotomy); Holter monitoring, exercise testing
Infective endocarditis	Lifelong risk; patient and family education on dental hygiene, antibiotic prophylaxis
Exercise counselling	Individualised based on repair type and haemodynamics; Fontan patients generally tolerate moderate exercise but may have significantly reduced exercise capacity
Pregnancy counselling	Female patients reaching reproductive age need pre-conception cardiac assessment; Fontan circulation carries significant maternal and fetal risk
Neurodevelopmental follow-up	Neonatal cyanosis + cardiac surgery → ↑ risk of developmental delay; developmental screening at standard intervals

Scenario	Emergency	Initial Palliation	Definitive
PAIVS, adequate RV, no RVDCC	PGE1 ± balloon septostomy	May proceed directly to catheter intervention	Transcatheter PV perforation + balloon valvuloplasty (valvular) or surgical RVOT reconstruction (infundibular) ± temporary shunt ^[1]
PAIVS, hypoplastic RV or RVDCC	PGE1 ± balloon septostomy	mBTS or PDA stent	Staged Fontan (Glenn → Fontan) ^[1]
PAVSD, confluent PAs	PGE1	mBTS	VSD closure + RV-PA conduit
PAVSD, MAPCAs	PGE1 if duct-dependent	mBTS or MAPCA management	Staged unifocalisation + VSD closure + RV-PA conduit

High Yield Summary — Management of Pulmonary Atresia

Emergency: IV PGE1 (alprostadil) to maintain ductal patency — start immediately upon suspicion; side effects: FAD (Fever, Apnoea, Diarrhoea) ^[1]^[6]
Balloon atrial septostomy if restrictive PFO in PAIVS ^[1]
Modified BT shunt is the workhorse palliative procedure for duct-dependent pulmonary circulation — always listen for shunt murmur on follow-up; blocked shunt can kill ^[1]^[3]
PAIVS definitive strategy determined by two questions: (a) Is there RVDCC? (b) Is the RV adequate?
RVDCC = absolute contraindication to RV decompression → must go Fontan pathway ^[1]
Valvular PAIVS without RVDCC → transcatheter perforation + balloon valvuloplasty ^[1]
Infundibular PAIVS → surgical RVOT reconstruction ^[1]
PAVSD requires unifocalisation of MAPCAs → connect all pulmonary blood supply into one tree → then VSD closure + RV-PA conduit
Avoid ACEI/ARB in R→L shunt lesions — ↓SVR worsens cyanosis ^[3]
All patients require lifelong cardiac follow-up: conduit replacement, arrhythmia surveillance, IE prophylaxis, neurodevelopmental monitoring

Active Recall - Management of Pulmonary Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 200, 218, 222) ^[3] Senior notes: Ryan Ho Cardiology.pdf (pages 188, 194) ^[6] Senior notes: Maksim Paediatric Notes.pdf (pages 55–56) ^[7] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (page 284)

Complications of Pulmonary Atresia

Complications of pulmonary atresia can be organised into three temporal categories: (1) complications of the untreated/pre-operative disease itself, (2) early post-operative/peri-procedural complications, and (3) late/long-term complications. Many of these are shared with other cyanotic congenital heart diseases, because the underlying pathophysiology — chronic hypoxaemia, abnormal haemodynamics, prosthetic materials, and surgical scars — is common to all.

1. Complications of the Untreated Disease (Pre-Operative)

These complications arise directly from the pathophysiology of pulmonary atresia — namely, chronic cyanosis and inadequate pulmonary blood flow (in duct-dependent subtypes) or excessive pulmonary blood flow (in PAVSD with unrestricted MAPCAs).

This is the most immediate and catastrophic complication.

Rapid clinical deterioration after ductal closure → uniformly fatal if untreated (~50% die ≤ 2 weeks, 85% die < 6 months) ^[1]

Mechanism: The PDA is the sole source of pulmonary blood flow in PAIVS and in PAVSD without adequate MAPCAs. Ductal closure (mediated by rising PaO₂ and falling circulating PGE₂) eliminates pulmonary blood flow → severe metabolic acidosis and hypoxaemia → seizures → cardiogenic shock, cardiac arrest, death ^[1].

Why metabolic acidosis? Without pulmonary blood flow, virtually no gas exchange occurs. Tissues become profoundly hypoxic → switch to anaerobic glycolysis → lactic acid accumulates → metabolic acidosis with a rising lactate gap. The acidosis itself further depresses myocardial contractility, creating a vicious cycle.

Why seizures? The brain is exquisitely sensitive to hypoxia. Profound cerebral hypoxia leads to neuronal depolarisation, excitotoxicity, and seizure activity. These seizures may also be compounded by the metabolic acidosis and hypoglycaemia that often accompany cardiogenic shock.

Even when the duct remains partially patent or MAPCAs provide some pulmonary flow, chronic suboptimal oxygenation leads to a constellation of systemic complications. These are shared with all cyanotic CHD ^[1]^[9]:

Complication	Mechanism	Clinical Details
Polycythaemia (reactive erythrocytosis)	Chronic hypoxaemia → ↑ renal EPO secretion → ↑ erythropoiesis → ↑ Hb and Hct	Haematocrit may exceed 65–70%. While initially compensatory (↑ O₂-carrying capacity), excessive polycythaemia increases blood viscosity → paradoxically impairs O₂ delivery. In children, relative iron deficiency is common (iron used up for excessive erythropoiesis) → microcytic, hypochromic red cells that are more rigid and deformable → further ↑ viscosity
Hyperviscosity symptoms	↑ viscosity from polycythaemia	Headache, dizziness, visual disturbances, fatigue, myalgia. In neonates/infants: irritability, poor feeding, lethargy
Stunted growth and failure to thrive	Chronic hypoxia → ↑ metabolic demand + ↓ tissue oxygen delivery → ↓ energy available for growth; also poor feeding due to tachypnoea and fatigue	"Stunted growth from hypoxia" ^[9]. Height and weight should be plotted on growth charts at every visit. This is a core paediatric concern — growth is the most sensitive indicator of well-being in children
Clubbing	Chronic hypoxaemia → release of PDGF and VEGF from megakaryocyte fragments bypassing the lung filter (in R→L shunt) → digital soft tissue hypertrophy and new vessel formation	Usually develops after months of sustained cyanosis; degree correlates with duration and severity of hypoxaemia
Cerebral complications: abscess and thromboembolic stroke	"Cerebral embolism/abscess" ^[1]^[9]: (a) Paradoxical embolism — in R→L shunt, venous thrombi or bacteria bypass the lung filter and enter the systemic arterial circulation → can lodge in the brain. (b) Polycythaemia + dehydration → cerebral venous sinus thrombosis. (c) Brain abscess — bacteraemia that bypasses the pulmonary capillary filter (which normally traps and clears bacteria) → seeds in the brain	Brain abscess is rare but classic in cyanotic CHD. Typically presents with headache, fever, focal neurological signs, seizures. Most common organisms: Streptococcus, anaerobes. Must maintain a high index of suspicion in any cyanotic CHD child with new neurological symptoms or fever
Coagulopathy	Chronic cyanosis → consumptive coagulopathy (↓ clotting factors, ↓ platelets) + hyperviscosity → paradoxical bleeding tendency despite thrombotic tendency	↑ risk of bleeding during surgery; need preoperative assessment of coagulation

Why Do Cyanotic CHD Patients Get Brain Abscesses?

Normally, the pulmonary capillary bed acts as a "filter" — bacteria entering the venous system are trapped and cleared in the lungs by alveolar macrophages and the reticuloendothelial system. In cyanotic CHD with R→L shunting, venous blood bypasses this filter and enters the systemic arterial circulation directly. If there is transient bacteraemia (e.g., from dental procedures, skin infection), bacteria can seed end-organs — particularly the brain, which has high blood flow and is susceptible. This is why IE prophylaxis and dental hygiene are so important in these patients.

"Infective endocarditis" is a risk in virtually all forms of CHD, including pulmonary atresia (both repaired and unrepaired) ^[1]^[9].

Why are PA patients at high risk?

Turbulent flow across abnormal valves (regurgitant tricuspid valve in PAIVS), VSD (in PAVSD), and surgical shunts/conduits damages the endothelium → exposes subendothelial collagen → platelet-fibrin deposition → nidus for bacterial colonisation
Prosthetic material (Gore-Tex shunts, RV-PA conduits, patches) provides a foreign surface for biofilm formation
R→L shunting allows venous organisms to access the arterial circulation

Common organisms in paediatric IE:

Streptococcus viridans group (most common after dental procedures)
Staphylococcus aureus (especially with indwelling lines or recent surgery)
Coagulase-negative staphylococci (prosthetic material)
HACEK organisms (less common)

Prevention:

Antibiotic prophylaxis before dental procedures and other high-risk procedures — lifelong in patients with prosthetic material, conduits, residual shunts, or unrepaired cyanotic CHD
Dental hygiene education — families must understand that good oral health is cardiac health

This is relevant specifically to PAVSD where unrestricted MAPCAs deliver systemic-pressure blood to the pulmonary vasculature → pulmonary hypertension ^[1].

Complications of Eisenmenger syndrome ^[1]^[9]:

Cardiac: progressive right heart failure, arrhythmia, IE (rare)
Pulmonary: pulmonary artery thrombosis, massive haemoptysis due to rupture of major vessel
Systemic: stunted growth from hypoxia, polycythaemia, cerebral embolism/abscess

Why does this happen from first principles? Unrestricted MAPCAs deliver blood at aortic pressure directly to pulmonary arterioles. These delicate vessels are designed to handle low pressures (~15–25 mmHg). Chronic exposure to systemic pressures (~70–100 mmHg in neonates) causes medial hypertrophy → intimal fibrosis → plexiform lesions in the pulmonary arterioles. Once these changes become irreversible (Heath-Edwards Grade IV–VI), PVR is fixed and elevated → Eisenmenger physiology.

Eisenmenger in PAVSD — An Important Distinction

In classic VSD-related Eisenmenger, the entire pulmonary vascular bed is uniformly exposed to high pressure. In PAVSD with MAPCAs, the exposure is heterogeneous — some lung segments (supplied by stenosed MAPCAs or native PAs) may be protected, while others (supplied by unrestricted MAPCAs) develop irreversible pulmonary vascular disease. This makes surgical planning extremely complex and is one reason why meticulous MAPCA mapping is essential.

In PAVSD with unrestricted MAPCAs (or after excessive surgical shunting), the pulmonary vascular bed is exposed to systemic-pressure blood → pulmonary hypertension ^[1].

Why it matters clinically: If pulmonary hypertension develops and is not addressed, it becomes irreversible and precludes definitive repair (because closing the VSD would force all RV output into a high-resistance pulmonary circuit → RV failure).

2. Early Post-Operative / Peri-Procedural Complications

These arise in the immediate period after surgical or catheter-based interventions.

Complication	Mechanism	Presentation/Management
Shunt thrombosis	Gore-Tex graft is a foreign surface → platelet activation and thrombus formation; more common in smaller grafts and in dehydrated/polycythaemic patients	Acute profound cyanosis + loss of continuous murmur ^[3] → medical emergency; heparinisation, urgent re-exploration or catheter intervention. Prevention: low-dose aspirin 3–5 mg/kg/day
Shunt overflow	Graft too large for patient → excessive L→R shunting	Heart failure, pulmonary oedema, poor diastolic coronary perfusion (coronary steal — diastolic runoff into pulmonary circulation)
Pulmonary artery distortion	Mechanical traction or kinking at the PA anastomosis site	Stenosis of ipsilateral PA → unequal lung perfusion; may need balloon angioplasty at catheterisation
Chylothorax	Damage to thoracic duct during surgical dissection	Milky pleural effusion; managed with chest drain, medium-chain triglyceride (MCT) diet, octreotide
Phrenic nerve palsy	Injury during thoracotomy	Ipsilateral diaphragm paralysis → respiratory compromise; more significant in neonates (less respiratory reserve)

Complication	Mechanism
RV perforation (during PV perforation in PAIVS)	Wire or RFA probe penetrates the thin RV wall → cardiac tamponade
Vascular injury	Femoral artery/vein damage during catheter access — particularly in small neonates
PDA stent migration	Stent displaces from the ductus → embolises to PA or aorta
Arrhythmia	Catheter irritation of the conduction system

Complication	Mechanism	Paediatric Considerations
Cardiopulmonary bypass (CPB) complications	Systemic inflammatory response, coagulopathy, capillary leak, neurological injury	Neonates are particularly vulnerable — immature coagulation, greater susceptibility to CPB-related brain injury
Low cardiac output syndrome	Post-CPB myocardial stunning; inadequate repair; residual shunts	Presents 6–24h post-op with tachycardia, poor perfusion, rising lactate; managed with inotropes (milrinone is often first-line in paediatric cardiac surgery — it is an inodilator that reduces afterload while augmenting contractility)
Junctional ectopic tachycardia (JET)	Post-operative arrhythmia from oedema/inflammation near the AV node and His bundle	Most common post-operative arrhythmia after congenital heart surgery; rate > 170–200 bpm; managed with cooling, amiodarone, temporary pacing
Heart block	Surgical damage to the conduction system (especially near VSD patch)	May require temporary or permanent pacing
Residual defects	Incomplete repair — residual VSD, residual RVOT obstruction	Detected by post-operative echo; may need re-intervention
Pleural effusions / chylothorax	Surgical dissection, increased central venous pressure	Common after Fontan; managed with drainage, MCT diet

3. Late / Long-Term Complications

These are the complications that define the grown-up congenital heart disease (GUCH) burden. All patients with PA require lifelong follow-up.

A. After Biventricular Repair (PAIVS or PAVSD)

This is the principal late complication after any RVOT reconstruction, analogous to post-TOF repair ^[3].

"Pulmonary regurgitation as principal late complication — cause: ↑ aggressive repair → ↑ risk of PV damage (especially if transannular patch used → obligatory PR)" ^[3]

Mechanism: During surgical RVOT reconstruction, the surgeon must relieve the outflow tract obstruction. If a transannular patch is used (the incision crosses the pulmonary valve annulus), the valve is rendered incompetent by definition → obligatory PR. Even without a transannular patch, the native valve may be damaged or absent.

Consequences of chronic PR ^[3]:

RV dilation and dysfunction — chronic volume overload (regurgitant blood returns to the RV in diastole → RV must handle extra volume with each beat → progressive dilation → eventually fails)
Decreased exercise tolerance — RV cannot augment cardiac output during exercise
Arrhythmia (VT, atrial flutter, AF) — dilated RV stretches the myocardium → creates substrate for re-entrant circuits
Sudden cardiac death — most feared late complication; usually from ventricular tachycardia/fibrillation arising from the dilated, scarred RV

Management of PR ^[3]:

Pulmonary valve replacement (PVR) when:
- MRI shows RV enlargement + > 25% regurgitant fraction ^[3]
- Symptomatic (RV failure, arrhythmia) ^[3]
Long-term follow-up and exercise testing every 3–4 years ^[3]

Issue	Explanation
Conduit stenosis	Homografts calcify over time; bovine conduits (Contegra) develop intimal peel formation → progressive obstruction
Conduit insufficiency	Valve within conduit degenerates → regurgitation
Outgrowing the conduit	Child grows but the conduit does not → relative stenosis; virtually all patients need at least one conduit replacement during childhood/adolescence
Management	Serial echo ± MRI; transcatheter pulmonary valve implantation (Melody valve or Sapien valve) in suitable anatomy; surgical conduit replacement if catheter approach not feasible

Transcatheter pulmonary valve implantation (TPVI) — e.g., the Melody valve — has transformed the management of conduit dysfunction. It allows a new valve to be placed inside the failing conduit via a catheter, avoiding repeat sternotomy. However, it requires a conduit of appropriate size and shape, and not all patients are candidates.

The Fontan circulation is a non-physiological state: it relies on passive venous flow through the lungs without a subpulmonary pump. Central venous pressure (CVP) is chronically elevated (~12–15 mmHg vs normal ~5–8 mmHg) to drive flow through the pulmonary vasculature. This has far-reaching consequences:

Complication	Mechanism	Clinical Features
Fontan failure (low cardiac output)	The single ventricle has limited ability to augment cardiac output; chronically elevated CVP → ↓ preload to the systemic ventricle → ↓ CO	Exercise intolerance, fatigue, oedema, ascites; progressive over years; ultimately may require heart transplant
Protein-losing enteropathy (PLE)	Chronically elevated CVP → elevated mesenteric venous pressure → lymphatic congestion in the gut wall → loss of protein (albumin, immunoglobulins) into the intestinal lumen	Diarrhoea, oedema, ascites, recurrent infections (↓ immunoglobulins), hypoalbuminaemia; carries a poor prognosis (5-year survival ~50% from diagnosis)
Plastic bronchitis	Lymphatic congestion → excessive secretion of proteinaceous casts into the bronchial tree → airway obstruction	Expectoration of branching bronchial casts; cough, dyspnoea, respiratory distress; rare but potentially fatal
Fontan-associated liver disease (FALD)	Chronically elevated hepatic venous pressure → hepatic congestion → fibrosis → cirrhosis	Elevated GGT, transaminases; progressive hepatic fibrosis on imaging; risk of hepatocellular carcinoma (HCC) in adulthood; all Fontan patients need liver surveillance
Thromboembolic events	Low-flow state in the Fontan circuit → stasis → thrombosis; also loss of coagulation factors (in PLE) and liver synthetic dysfunction → paradoxical hypo- and hypercoagulability	Stroke, PE, Fontan pathway thrombosis; many centres anticoagulate Fontan patients (warfarin or aspirin — practice varies)
Arrhythmias	Atrial dilation, surgical scars, chronically elevated atrial pressure → substrate for re-entrant atrial tachyarrhythmias (atrial flutter, intra-atrial re-entrant tachycardia)	Palpitations, syncope, Fontan failure exacerbation; managed with antiarrhythmics, catheter ablation, or pacemaker
Cyanosis (persistent mild)	Residual R→L shunting via fenestrations, hepatic vein to pulmonary vein collaterals, or bronchial venous drainage	SpO₂ typically 90–95% even after Fontan; not usually clinically significant unless it worsens
Neurodevelopmental delay	Cumulative effect of neonatal hypoxia, multiple surgeries, prolonged ICU stays, CPB-related brain injury	Affects cognitive, motor, and psychosocial development; neurodevelopmental assessment should be part of routine follow-up

Fontan is a Palliation, Not a Cure

It is critical to communicate to families that the Fontan operation, while life-saving, creates a non-physiological circulation with inevitable long-term complications. Approximately 40% of Fontan patients will develop significant complications by 20–30 years post-Fontan. Heart transplantation remains the ultimate treatment for Fontan failure, but donor availability is a major limiting factor, particularly in Hong Kong.

Complication	Details
Infective endocarditis	Lifelong risk — prosthetic material (patches, conduits, shunts) provides nidus for infection; antibiotic prophylaxis before dental procedures is mandatory; families must be educated about dental hygiene and the need to report unexplained fevers
Arrhythmias	Both atrial (flutter, fibrillation, IART) and ventricular (VT, VF); arise from surgical scars, myocardial fibrosis, chamber dilation; require Holter monitoring, exercise testing, and in some cases ICD implantation
Sudden cardiac death	The most feared late outcome; related to ventricular arrhythmias from RV dilation/dysfunction/scarring; annual risk ~0.1–0.5% after repair; risk factors include QRS duration > 180 ms, severe PR, RV dysfunction
Exercise limitation	Even after good repair, most PA patients have reduced exercise capacity compared to healthy peers; exercise prescription should be individualised based on haemodynamic assessment
Pregnancy risk	Female patients of reproductive age need pre-conception cardiac assessment; Fontan circulation carries significant maternal risk (heart failure, arrhythmia, thromboembolism) and fetal risk (prematurity, IUGR, miscarriage); pregnancy is contraindicated in Eisenmenger syndrome (maternal mortality 30–50%) ^[1]^[9]
Psychosocial impact	Chronic illness, surgical scars, exercise restriction, lifelong medical follow-up → impact on self-esteem, social functioning, and mental health; psychological support should be integrated into care
Neurodevelopmental issues	↑ risk of cognitive delay, learning difficulties, attention deficit, and motor delay — related to chronic hypoxia, CPB, and prolonged hospitalisations; routine developmental screening is essential

System	Specific Complications
Cardiovascular	RV failure, arrhythmia (VT/VF, atrial flutter), conduit stenosis/degeneration, PR, IE, sudden cardiac death, Fontan failure
Pulmonary	Pulmonary hypertension (from unrestricted MAPCAs), PA thrombosis, massive haemoptysis (Eisenmenger), plastic bronchitis (Fontan)
Haematological	Polycythaemia, hyperviscosity, coagulopathy, iron deficiency
Neurological	Cerebral abscess, thromboembolic stroke, neurodevelopmental delay, seizures (from hypoxia)
Hepatic	Fontan-associated liver disease → fibrosis → cirrhosis → HCC risk
Gastrointestinal	Protein-losing enteropathy (Fontan)
Growth/Development	Stunted growth, failure to thrive, delayed puberty
Infectious	IE, brain abscess, recurrent infections (if PLE → immunoglobulin loss)
Reproductive	High-risk pregnancy (especially Fontan, Eisenmenger — contraindicated)

High Yield Summary — Complications of Pulmonary Atresia

Untreated PA is uniformly fatal: ~50% die within 2 weeks, 85% within 6 months without intervention ^[1]
Ductal closure → profound hypoxaemia, metabolic acidosis, seizures, cardiogenic shock, death ^[1]
Chronic cyanosis → polycythaemia, hyperviscosity, clubbing, stunted growth, cerebral abscess/stroke ^[1]^[9]
Brain abscess — unique to cyanotic CHD: R→L shunt bypasses the pulmonary capillary filter → bacteria seed the brain
IE — lifelong risk from prosthetic material and abnormal flow; requires prophylaxis and dental hygiene education
Eisenmenger syndrome — from unrestricted MAPCAs in PAVSD; irreversible pulmonary vascular disease; complications include RHF, haemoptysis, arrhythmia ^[1]^[9]
Post-repair PR is the principal late complication → RV dilation → dysfunction → arrhythmia → sudden death; managed by PVR when MRI shows > 25% regurgitant fraction or symptoms ^[3]
Blocked BT shunt — acute cyanosis + loss of murmur = emergency ^[3]
Fontan complications: low cardiac output, PLE, plastic bronchitis, FALD, thromboembolism, arrhythmia
Neurodevelopmental delay — cumulative effect of hypoxia, surgery, CPB; mandates routine developmental screening
Pregnancy is contraindicated in Eisenmenger syndrome (maternal mortality 30–50%) ^[1]^[9]

Active Recall - Complications of Pulmonary Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 53, 56, 193, 218) ^[3] Senior notes: Ryan Ho Cardiology.pdf (pages 186, 188, 191) ^[9] Senior notes: Ryan Ho Cardiology.pdf (page 186) — Eisenmenger complications

High Yield Summary

Pulmonary Atresia — Key Points for Exams:

Two distinct entities: PAIVS (no VSD, hypoplastic RV, duct-dependent) vs PAVSD (VSD present, extreme TOF variant, ± MAPCAs)
Both are duct-dependent cyanotic heart diseases → present with cyanosis within hours of birth; failed hyperoxia test; oligaemic lung fields
PAIVS: Single S2, NO RV impulse (LV impulse instead), PSM from TR, soft PDA murmur; ECG shows LV dominance; 1/3 have ventriculo-coronary fistulae; 1/4 of those have RVDCC (precludes biventricular repair)
PAVSD: Single S2, NO PS murmur (unlike TOF), ± continuous MAPCA murmur; ECG shows RAD + RVH; boot-shaped heart on CXR
Immediate management: IV prostaglandin E1 (alprostadil) to maintain ductal patency
PAIVS mortality without treatment: ~50% by 2 weeks, 85% by 6 months
MAPCAs in PAVSD: if stenosed → cyanosis/shock; if unrestricted → pulmonary hypertension/HF
CXR clue for cyanotic CHD vs respiratory: oligaemic lung fields + cyanosis = cardiac cause
ECG distinction: PAIVS = LV dominance; PAVSD = RVH + RAD
RVDCC = contraindication to biventricular repair → must go Fontan pathway

High Yield Summary — DDx of Pulmonary Atresia

First distinguish cardiac from non-cardiac cyanosis: hyperoxia test (PaO₂ < 100–150 on 100% FiO₂ = cardiac); oligaemic lung fields on CXR support cardiac cause ^[4]
PPHN mimics cyanotic CHD — differentiate by Echo showing structurally normal heart
Categorise cyanotic CHD by pulmonary blood flow ^[5]: ↓ pulmonary flow (oligaemic) vs ↑ flow (plethoric) vs severe HF
PA sits in the ↓ pulmonary blood flow group alongside TOF, tricuspid atresia, critical PS, and Ebstein's
PAVSD vs TOF: no PS murmur in PA (no flow = no murmur); PAVSD is the extreme end of the TOF spectrum ^[1]
PAIVS vs PAVSD: intact septum, hypoplastic RV, LV dominance on ECG, PSM from TR (PAIVS) vs VSD present, RVH on ECG, ± MAPCAs (PAVSD)
PAIVS vs Critical PS: nearly identical clinically; Echo shows no antegrade PV flow in PAIVS vs tiny jet in critical PS; critical PS is amenable to balloon valvuloplasty ^[7]
Tricuspid atresia: classic LAD on ECG (vs LV dominance without LAD in PAIVS)
Ebstein's: massive cardiomegaly disproportionate to symptoms; WPW on ECG in ~20%
Always check for syndromes: 22q11.2 (PAVSD), Noonan (dysplastic PS), Alagille (peripheral PS)

High Yield Summary — Investigations in Pulmonary Atresia

Pulse oximetry screening at 24–48h of life detects CCHD before ductal closure; SpO₂ < 90% → immediate evaluation
Hyperoxia test: PaO₂ < 100–150 mmHg on 100% FiO₂ = fixed R→L shunt = cardiac cause; do not delay PGE1 for this test
CXR in PAIVS: variable heart size ± massive RA; diminished pulmonary vascular markings ^[1]
CXR in PAVSD: boot-shaped heart; oligaemic or uneven lung fields ^[1]
"Oligaemic lung field supports cyanotic CHD over respiratory disease" ^[4]
ECG — the key differentiator: PAIVS = LV dominance (abnormal for a neonate); PAVSD = RAD + RVH ^[1]
Echo is the definitive diagnostic tool: confirms anatomy, assesses RV size (TV Z-score), detects ventriculo-coronary sinusoidal flow ^[1]
MAPCAs cannot be fully mapped by Echo → detailed delineation only by MRI or cardiac catheterisation ^[1]
Cardiac catheterisation is the gold standard for detecting RVDCC in PAIVS — determines whether biventricular repair is safe
22q11.2 genetic testing is mandatory in PAVSD, especially with MAPCAs

High Yield Summary — Management of Pulmonary Atresia

Emergency: IV PGE1 (alprostadil) to maintain ductal patency — start immediately upon suspicion; side effects: FAD (Fever, Apnoea, Diarrhoea) ^[1]^[6]
Balloon atrial septostomy if restrictive PFO in PAIVS ^[1]
Modified BT shunt is the workhorse palliative procedure for duct-dependent pulmonary circulation — always listen for shunt murmur on follow-up; blocked shunt can kill ^[1]^[3]
PAIVS definitive strategy determined by two questions: (a) Is there RVDCC? (b) Is the RV adequate?
RVDCC = absolute contraindication to RV decompression → must go Fontan pathway ^[1]
Valvular PAIVS without RVDCC → transcatheter perforation + balloon valvuloplasty ^[1]
Infundibular PAIVS → surgical RVOT reconstruction ^[1]
PAVSD requires unifocalisation of MAPCAs → connect all pulmonary blood supply into one tree → then VSD closure + RV-PA conduit
Avoid ACEI/ARB in R→L shunt lesions — ↓SVR worsens cyanosis ^[3]
All patients require lifelong cardiac follow-up: conduit replacement, arrhythmia surveillance, IE prophylaxis, neurodevelopmental monitoring

High Yield Summary — Complications of Pulmonary Atresia

Untreated PA is uniformly fatal: ~50% die within 2 weeks, 85% within 6 months without intervention ^[1]
Ductal closure → profound hypoxaemia, metabolic acidosis, seizures, cardiogenic shock, death ^[1]
Chronic cyanosis → polycythaemia, hyperviscosity, clubbing, stunted growth, cerebral abscess/stroke ^[1]^[9]
Brain abscess — unique to cyanotic CHD: R→L shunt bypasses the pulmonary capillary filter → bacteria seed the brain
IE — lifelong risk from prosthetic material and abnormal flow; requires prophylaxis and dental hygiene education
Eisenmenger syndrome — from unrestricted MAPCAs in PAVSD; irreversible pulmonary vascular disease; complications include RHF, haemoptysis, arrhythmia ^[1]^[9]
Post-repair PR is the principal late complication → RV dilation → dysfunction → arrhythmia → sudden death; managed by PVR when MRI shows > 25% regurgitant fraction or symptoms ^[3]
Blocked BT shunt — acute cyanosis + loss of murmur = emergency ^[3]
Fontan complications: low cardiac output, PLE, plastic bronchitis, FALD, thromboembolism, arrhythmia
Neurodevelopmental delay — cumulative effect of hypoxia, surgery, CPB; mandates routine developmental screening
Pregnancy is contraindicated in Eisenmenger syndrome (maternal mortality 30–50%) ^[1]^[9]

Pulmonary Atresia

Definition

Epidemiology

Risk Factors

General CHD risk factors (apply to both subtypes)

Specific associations

Anatomy and Embryology

Normal Cardiac Development (to understand what goes wrong)

What goes wrong in Pulmonary Atresia

PAVSD (PA with VSD) — "Extreme TOF"

PAIVS (PA with Intact Ventricular Septum)

Normal structures the neonate relies on

Aetiology (with Hong Kong focus) and Pathophysiology

Classification

A. Pulmonary Atresia with VSD (PAVSD / TOF with Pulmonary Atresia)

Pathophysiology — Step by Step

MAPCAs — Understanding them from first principles

Haemodynamic consequences

B. Pulmonary Atresia with Intact Ventricular Septum (PAIVS)

Pathophysiology — Step by Step

The Spectrum of RV Size in PAIVS

Classification Summary

Clinical Features

A. Symptoms

1. Cyanosis (both PAIVS and PAVSD)

2. Rapid Clinical Deterioration After Ductal Closure (especially PAIVS)

3. Heart Failure (specific situations)

4. Feeding Difficulty and Failure to Thrive

B. Signs

PAIVS — Physical Examination Findings

PAVSD — Physical Examination Findings

Comparison of Auscultatory Findings

C. Clues from the Clinical Scenario (for exam purposes)

Investigations (Preview)

PAIVS [1]

PAVSD [1]

Relevant Associations and Syndromes

Summary of Pathophysiological Concepts

Active Recall - Pulmonary Atresia: Definition, Epidemiology, Pathophysiology and Clinical Features

References

Framing the DDx Problem

Step 1: Cardiac vs Non-Cardiac Cyanosis

Step 2: Within Cyanotic CHD — Categorise by Pulmonary Blood Flow

A. Cyanotic CHD with Decreased Pulmonary Blood Flow (Oligaemic Lung Fields)

B. Cyanotic CHD with Increased Pulmonary Blood Flow (Plethoric Lung Fields) — the "3 Ts"

C. Cyanotic CHD with Severe Heart Failure (Duct-Dependent Systemic Circulation)

Step 3: Differentiating PAIVS from PAVSD

Differential Diagnosis Algorithm

Specific DDx Comparisons — Why Each Mimic is Different

1. Pulmonary Atresia vs Tetralogy of Fallot

2. Pulmonary Atresia vs Tricuspid Atresia

3. Pulmonary Atresia vs Ebstein's Anomaly

4. Pulmonary Atresia vs TGA

Mnemonic for Cyanotic CHD with Decreased Pulmonary Blood Flow

Syndrome-Based DDx Clues

Summary Table: Key DDx of Cyanotic Neonate (Exam-Ready)

Active Recall - Differential Diagnosis of Pulmonary Atresia

Diagnostic Criteria

The Diagnostic Approach — From Bedside to Definitive Diagnosis

Phase 1: Recognition — Pulse Oximetry Screening

Phase 2: Differentiation — Cardiac vs Non-Cardiac Cyanosis

A. The Hyperoxia Test (Nitrogen Washout Test)

B. Pre-Ductal vs Post-Ductal SpO₂ Comparison

C. Chest X-Ray (CXR) — First-Line Imaging

Phase 3: Anatomical Diagnosis — Echocardiography

Investigation Modalities — Detailed Findings and Interpretation

1. Chest X-Ray (CXR)

PAIVS [1]

PAVSD [1]

2. Electrocardiogram (ECG)

PAIVS [1]

PAVSD [1]

3. Echocardiography — The Definitive Diagnostic Tool

PAIVS — Echocardiographic Findings [1]

PAVSD — Echocardiographic Findings [1]

4. CT Angiography (CTA)

5. Cardiac MRI

6. Cardiac Catheterisation

Diagnostic catheterisation provides:

Therapeutic catheterisation (covered more in management, but important to know here):